Update README

Pin to latest `v1` action.

Author: ethomson

README.md

@@ -16,18 +16,18 @@ See [action.yml](action.yml)
 Basic:
 ```yaml
 steps:
-- uses: actions/checkout@latest
+- uses: actions/checkout@v1
 - uses: actions/setup-java@v1
   with:
-    java-version: '9.0.4' // The JDK version to make available on the path. Takes a whole or semver Jdk version, or 1.x syntax (e.g. 1.8 => Jdk 8.x)
+    java-version: '9.0.4' // The JDK version to make available on the path. Takes a whole or semver JDK version, or 1.x syntax (e.g. 1.8 => JDK 8.x)
     architecture: x64 // (x64 or x86) - defaults to x64
 - run: java -cp java HelloWorldApp
 ```
 
 From local file:
 ```yaml
 steps:
-- uses: actions/checkout@master
+- uses: actions/checkout@v1
 - uses: actions/setup-java@v1
   with:
     java-version: '4.0.0'