fix: ensure SemVer instanced passed as input are not modified

Author: louis-bompart

Diff for: functions/inc.js

@@ -7,7 +7,10 @@ const inc = (version, release, options, identifier) => {
   }
 
   try {
-    return new SemVer(version, options).inc(release, identifier).version
+    return new SemVer(
+      version instanceof SemVer ? version.version : version,
+      options
+    ).inc(release, identifier).version
   } catch (er) {
     return null
   }