[lint] Use sys.exit() instead of exit()

- Coming from Pylnt v2.4.0
- https://github.com/PyCQA/pylint/blob/master/ChangeLog

examples/save_and_load_private_key_file.py

 from duniterpy.key import SigningKey
 import getpass
 import os
+import sys
 
 if "XDG_CONFIG_HOME" in os.environ:
     home_path = os.environ["XDG_CONFIG_HOME"]
@@ -35,7 +36,7 @@ signer = SigningKey.from_credentials(salt, password)
 # check public key
 if signer.pubkey != pubkey:
     print("Bad credentials!")
-    exit(1)
+    sys.exit(1)
 
 # save private keys in a file (json format)
 signer.save_private_key(PRIVATE_KEYS_FILE_PATH)
@@ -49,4 +50,4 @@ loaded_signer = SigningKey.from_private_key(PRIVATE_KEYS_FILE_PATH)  # type: Sig
 # check public key from file
 print("Public key %s loaded from file %s" % (pubkey, PRIVATE_KEYS_FILE_PATH))
 
-exit(0)
+sys.exit(0)

examples/save_and_load_private_key_file_ewif.py

 from duniterpy.key import SigningKey
 import getpass
 import os
+import sys
 
 if "XDG_CONFIG_HOME" in os.environ:
     home_path = os.environ["XDG_CONFIG_HOME"]
@@ -35,7 +36,7 @@ signer = SigningKey.from_credentials(salt, password)
 # check public key
 if signer.pubkey != pubkey:
     print("Bad credentials!")
-    exit(1)
+    sys.exit(1)
 
 # prompt hidden user entry
 ewif_password = getpass.getpass("Enter an encryption password: ")
@@ -62,7 +63,7 @@ try:
 
 except IOError as error:
     print(error)
-    exit(1)
+    sys.exit(1)
 
 
-exit(0)
+sys.exit(0)

examples/save_and_load_private_key_file_pubsec.py

 from duniterpy.key import SigningKey
 import getpass
 import os
+import sys
 
 if "XDG_CONFIG_HOME" in os.environ:
     home_path = os.environ["XDG_CONFIG_HOME"]
@@ -35,7 +36,7 @@ signer = SigningKey.from_credentials(salt, password)
 # check public key
 if signer.pubkey != pubkey:
     print("Bad credentials!")
-    exit(1)
+    sys.exit(1)
 
 # save private key in a file (PubSec v1 format)
 signer.save_pubsec_file(PRIVATE_KEY_FILE_PATH)
@@ -57,7 +58,7 @@ try:
 
 except IOError as error:
     print(error)
-    exit(1)
+    sys.exit(1)
 
 
-exit(0)
+sys.exit(0)

examples/save_and_load_private_key_file_wif.py

 from duniterpy.key import SigningKey
 import getpass
 import os
+import sys
 
 if "XDG_CONFIG_HOME" in os.environ:
     home_path = os.environ["XDG_CONFIG_HOME"]
@@ -35,7 +36,7 @@ signer = SigningKey.from_credentials(salt, password)
 # check public key
 if signer.pubkey != pubkey:
     print("Bad credentials!")
-    exit(1)
+    sys.exit(1)
 
 # save private key in a file (WIF v1 format)
 signer.save_wif_file(PRIVATE_KEY_FILE_PATH)
@@ -57,7 +58,7 @@ try:
 
 except IOError as error:
     print(error)
-    exit(1)
+    sys.exit(1)
 
 
-exit(0)
+sys.exit(0)

examples/save_revoke_document.py

 import asyncio
 import getpass
 import os
+import sys
 from typing import Optional
 
 import duniterpy.api.bma as bma
@@ -123,7 +124,7 @@ async def main():
     # check public key
     if signer.pubkey != pubkey:
         print("Bad credentials!")
-        exit(0)
+        sys.exit(0)
 
     # capture current block to get currency name
     current_block = await client(bma.blockchain.current)
@@ -134,7 +135,7 @@ async def main():
         print("Identity not found for pubkey {0}".format(pubkey))
         # Close client aiohttp session
         await client.close()
-        exit(1)
+        sys.exit(1)
 
     # get the revoke document
     revocation_signed_raw_document = get_signed_raw_revocation_document(

examples/send_certification.py

+import sys
 import asyncio
 import getpass
 from typing import Optional
@@ -114,7 +115,7 @@ async def main():
         print("Identity not found for pubkey {0}".format(pubkey_to))
         # Close client aiohttp session
         await client.close()
-        exit(1)
+        sys.exit(1)
 
     # send the Certification document to the node
     certification = get_certification_document(current_block, identity, pubkey_from)

examples/send_transaction.py

+import sys
 import asyncio
 import getpass
 
@@ -120,7 +121,7 @@ async def main():
 
     if len(response["sources"]) == 0:
         print("no sources found for account %s" % pubkey_to)
-        exit(1)
+        sys.exit(1)
 
     # get the first source
     source = response["sources"][0]