standardize console output

vars/bumpVersion.groovy

@@ -18,7 +18,8 @@ String call(String version, String flag = 'patch') {
             patch++
             break
         default:
-            echo "Invalid flag: $flag"
+            echo "Warning: Invalid increment flag for version increment: $flag"
+            echo 'Info: Flag value should be one of major, minor or patch.'
             return version
     }