Test on modern node runtimes

1. Increase timeout when run tests with coverage report to resolve following issues.

   https://travis-ci.org/Gasol/aglio/jobs/531855660

      1) Executable
           Should start a live preview server:
         Error: Timeout of 5000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/travis/build/Gasol/aglio/test/basic.coffee)
          at Timeout._onTimeout (test/basic.coffee:306:37)
          at listOnTimeout (internal/timers.js:531:17)
          at processTimers (internal/timers.js:475:7)

2. Keep the npm cache

   https://docs.travis-ci.com/user/caching/#npm-cache

.travis.yml

@@ -1,19 +1,24 @@
+dist: xenial
 language: node_js
-sudo: false
 node_js:
-    - "0.10"
-    - "0.12"
-    - "3"
-    - "4"
-    - "5"
-    - "6"
+  - "6"
+  - "8"
+  - "10"
+  - "11"
+  - "12"
+
 addons:
   apt:
     sources:
     - ubuntu-toolchain-r-test
     packages:
     - gcc-4.8
     - g++-4.8
-env: CXX="g++-4.8" CC="gcc-4.8"
+
+env:
+  - CXX="g++-4.8" CC="gcc-4.8"
+
 after_script:
-    - npm run coveralls
+  - if [ "$TRAVIS_NODE_VERSION" = "12" ]; then npm run coveralls; fi
+
+cache: npm

package.json

@@ -6,11 +6,14 @@
   "bin": {
     "aglio": "./bin/aglio.js"
   },
+  "config": {
+      "coverage_timeout": 10000
+  },
   "scripts": {
     "build": "npm run lint && npm run compile",
     "compile": "coffee -o lib -c src",
     "coverage": "npm run coverage:html",
-    "coverage:text": "npm run build && c8 mocha",
+    "coverage:text": "npm run build && c8 mocha -t $npm_package_config_coverage_timeout",
     "coverage:html": "npm run coverage:text && c8 -r html report",
     "coveralls": "npm run coverage:text && c8 -r text-lcov report | coveralls",
     "gen:examples": "npm run compile && ./scripts/generate-examples",

test/basic.coffee

@@ -271,7 +271,7 @@ describe 'Executable', ->
             done()
 
     it 'Should start a live preview server', (done) ->
-        @timeout 5000
+        @timeout process.env.npm_package_config_coverage_timeout || 5000
 
         sinon
             .stub aglio, 'render'