Fix #244 download Node.js only once when building from sources

install.sh

@@ -100,6 +100,7 @@ install_ucoin_from_git() {
   local NODEJS_TARBALL=http://nodejs.org/dist/v${NVER}/${NODEJS_FILENAME}.tar.gz
   local NODEJS_ARCHIVE=$UCOIN_DIR/node.tar.gz
   local NODEJS_EXTRACTED=$UCOIN_DIR/$NODEJS_FILENAME
+  if [ ! -d "$UCOIN_DIR/node" ]; then
     echo "=> Downloading '$NODEJS_TARBALL' to '$NODEJS_ARCHIVE'"
     ucoin_download "$NODEJS_TARBALL" -o "$NODEJS_ARCHIVE" || {
       echo >&2 "Failed to download '$NODEJS_TARBALL'"
@@ -113,6 +114,7 @@ install_ucoin_from_git() {
       echo >&2 "Failed to extract '$NODEJS_ARCHIVE'"
       return 6
     }
+  fi
 
   # Install uCoin dependencies (NPM modules)
   export PATH=$PATH:$UCOIN_DIR/node/bin/