Polish the README

Author: eregon

README.md

@@ -53,7 +53,7 @@ jobs:
 
 ### Supported Version Syntax
 
-* `engine-version` like `ruby-2.6.5` and `truffleruby-19.3.0`
+* engine-version like `ruby-2.6.5` and `truffleruby-19.3.0`
 * short version like `2.6`, automatically using the latest release matching that version (`2.6.5`)
 * version only like `2.6.5`, assumes MRI for the engine
 * engine only like `truffleruby`, uses the latest stable release of that implementation