Change black.vim error message to specify its origin.
diff --git a/plugin/black.vim b/plugin/black.vim
index 385d0e1bd98..b174e598452 100644
--- a/plugin/black.vim
+++ b/plugin/black.vim
@@ -14,7 +14,7 @@
 "    - restore cursor/window position after formatting
 
 if v:version < 700 || !has('python3')
-    echo "This script requires vim7.0+ with Python 3.6 support."
+    echo "The black.vim plugin requires vim7.0+ with Python 3.6 support."
     finish
 endif
 

Fixes #1230 .

This just changes the error message if the black.vim plugin is unable to load, to specify that it is coming from "The black.vim plugin" instead of "This script" when the user is viewing the message in vim.