Fix comment examples in README

Author: RichardBradley

README.md

@@ -108,9 +108,9 @@ Any matched classes will not be instrumented or included in the coverage report.
 
 You can also mark sections of code with comments like:
 
-    // $COVERAGE:OFF$
+    // $COVERAGE-OFF$
     ...
-    // $COVERAGE:ON$
+    // $COVERAGE-ON$
 
 Any code between two such comments will not be instrumented or included in the coverage report.