Build binaryen.js and wasm.js on Travis CI (#1260)

.travis.yml

@@ -57,6 +57,23 @@ jobs:
         CC_COMPILER="gcc-5"
         CXX_COMPILER="g++-5"
 
+    # Build the .js outputs using emcc
+    - &test-emcc
+      stage: test
+      compiler: clang
+      python: 2.7
+      node_js: 7
+      language: node_js
+      node_js:
+      - node
+      sudo: required
+      services:
+      - docker
+      before_install:
+      - docker run -dit --name emscripten -v $(pwd):/src trzeci/emscripten:sdk-incoming-64bit bash
+      script:
+      - docker exec -it emscripten bash ./build-js.sh -g
+
     # Build with gcc 6.3 and run tests on Alpine Linux (inside chroot).
     # Note: Alpine uses musl libc.
     - &test-alpine