Use full commit sha width for reference in note body to prevent Ambiguous SHA1 prefix problem

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/models/commit.rb

@@ -115,7 +115,7 @@ class Commit
 
   # Mentionable override.
   def gfm_reference
-    "commit #{short_id}"
+    "commit #{id}"
   end
 
   def method_missing(m, *args, &block)