Replace 'command' with 'utility' in README

Author: tommarshall

README.md

@@ -4,7 +4,7 @@
 
 Running `git diff` on files encrypted with ansible vault results in some pretty unhelpful output.
 
-`git-diff-ansible-vault` is custom git command that detects files encrypted with ansible vault within the diff, and safely decrypts them to reveal the true changes.
+`git-diff-ansible-vault` is custom git utility that detects files encrypted with ansible vault within the diff, and safely decrypts them to reveal the true changes.
 
 ![git-diff-ansible-vault animated demo](https://github.com/tommarshall/git-diff-ansible-vault/blob/master/img/demo.gif)