[enh] fix typo in cert error message

silkaj/cert.py

@@ -104,7 +104,7 @@ def pre_checks(client, issuer_pubkey, pubkey_to_certify):
     # Check if the certification is already in the pending certifications
     for pending_cert in req["pendingCerts"]:
         if pending_cert["from"] == issuer_pubkey:
-            sys.exit("Certification is currently been processed")
+            sys.exit("Certification is currently being processed")
     return issuer