fix formatting in core package readme (#563)

README.md

@@ -62,10 +62,10 @@ catch (err) {
   // setFailed logs the message and sets a failing exit code
   core.setFailed(`Action failed with error ${err}`);
 }
+```
 
 Note that `setNeutral` is not yet implemented in actions V2 but equivalent functionality is being planned.
 
-```
 
 #### Logging