Chore: FLOW command in makefile and logic in .travis.yml(issue#4710). (#4807)

.travis.yml

@@ -13,12 +13,15 @@ node_js:
 script: 
   - 'if [ -n "${LINT-}" ]; then make lint ; fi'
   - 'if [ -z "${LINT-}" ]; then make test-ci ; fi'
+  - 'if [ -n "${FLOW-}" ]; then make flow ; fi'
 
 matrix:
   fast_finish: true
   include:
     - node_js: "node"
-      env: LINT=true
+      env:
+        - LINT: true
+        - FLOW: true
       
 notifications:
   on_success: change

Makefile

@@ -20,6 +20,9 @@ watch: clean
 lint:
 	./node_modules/.bin/eslint packages/*/{src,test}/*.js --format=codeframe
 
+flow:
+	./node_modules/.bin/flow check
+
 fix:
 	./node_modules/.bin/eslint packages/*/{src,test}/*.js --format=codeframe --fix
 
@@ -54,7 +57,6 @@ test-cov: clean
 
 test-ci:
 	NODE_ENV=test make bootstrap
-	# if ./node_modules/.bin/semver `npm --version` -r ">=3.3.0"; then ./node_modules/.bin/flow check; fi
 	./scripts/test-cov.sh
 	cat ./coverage/coverage.json | ./node_modules/codecov.io/bin/codecov.io.js