skip _compat for instrumental

as the _compat module implements version specific code and we
can run instrumental in python2 only, skip it from consideration

Author: tomato42

.travis.yml

@@ -118,7 +118,7 @@ script:
       if [[ $INSTRUMENTAL && $TRAVIS_PULL_REQUEST != "false" ]]; then
         git checkout $PR_FIRST^
         files="$(ls src/ecdsa/test*.py)"
-        instrumental -t ecdsa -i 'test.*|.*_version' `which pytest` $files
+        instrumental -t ecdsa -i 'test.*|.*_version|.*_compat' `which pytest` $files
         instrumental -f .instrumental.cov -s
         instrumental -f .instrumental.cov -s | python diff-instrumental.py --save .diff-instrumental
         git checkout $BRANCH