fix: don’t throw error if failing to set new package.json value (#737)

lib/workers/branch/package-json.js

@@ -44,11 +44,11 @@ function setNewValue(currentFileContent, depType, depName, newVersion, logger) {
   }
   // istanbul ignore if
   if (!newFileContent) {
-    logger.debug(
+    logger.warn(
       { currentFileContent, parsedContents, depType, depName, newVersion },
       'setNewValue error'
     );
-    throw new Error('Could not set new value');
+    return currentFileContent;
   }
   return newFileContent;
 }