Try enabling coverage again

It was disabled in d138b286db.
We should have more Travis instances now so it shouldn't run out of memory.

.travis.yml

@@ -68,7 +68,12 @@ script:
       fi
     elif [ "$TEST_TYPE" = test ]; then
       set -e
-      ./node_modules/.bin/grunt jest:normal
+      if [ "$TRAVIS_PULL_REQUEST" = false ]; then
+        ./node_modules/.bin/grunt jest:coverage
+        cat ./coverage/lcov.info | ./node_modules/.bin/coveralls
+      else
+        ./node_modules/.bin/grunt jest:normal
+      fi
       echo 'Testing in server-render (HTML generation) mode...'
       printf '\nmodule.exports.useCreateElement = false;\n' \
         >> src/renderers/dom/shared/ReactDOMFeatureFlags.js