Add check-types to package.json (#627)

* Add type checking to ci

* Update @types/node to version 12

We are using node 12 on ci

* Add check-types to package.json

.travis.yml

@@ -11,5 +11,5 @@ install:
   - yarn
 
 script:
-  - tsc --noEmit
-  - xvfb-run --server-args="-screen 0 1920x1080x24" npm test
+  - yarn check-types
+  - xvfb-run --server-args="-screen 0 1920x1080x24" yarn test

package.json

@@ -11,7 +11,8 @@
     "repl": "npm run bundle:browser && cross-env TS_NODE_CACHE=false TS_NODE_FILES=true ts-node scripts/repl.ts",
     "bundle:browser": "cross-env BROWSER_ONLY=true rollup --config",
     "bundle": "rollup --config",
-    "typings": "tsc -d --declarationDir typings"
+    "typings": "tsc -d --declarationDir typings",
+    "check-types": "tsc -noEmit"
   },
   "repository": {
     "type": "git",