docs: remove gm library references from README

Author: angelcaamal

functions/v2/imagemagick/README.md

@@ -1,6 +1,6 @@
 <img src="https://avatars2.githubusercontent.com/u/2810941?v=3&s=96" alt="Google Cloud Platform logo" title="Google Cloud Platform" align="right" height="96" width="96"/>
 
-# Google Cloud Functions ImageMagick sample
+# Google Cloud Functions imagemagick sample
 
 This sample shows you how to blur an image using sharp in a
 Storage-triggered Cloud Function.