chore(flakiness): fix flakiness on Appveyour and Travis (#4827)

This patch fixes build URL on Appveyour and splits out
Firefox tests into a separate dashboard on Travis.

.appveyor.yml

@@ -10,7 +10,7 @@ environment:
 build: off
 
 install:
-  - ps: $env:FLAKINESS_DASHBOARD_BUILD_URL="https://ci.appveyor.com/project/aslushnikov/puppeteer/branch/master/job/$env:APPVEYOR_JOB_ID"
+  - ps: $env:FLAKINESS_DASHBOARD_BUILD_URL="https://ci.appveyor.com/project/aslushnikov/puppeteer/builds/$env:APPVEYOR_BUILD_ID/job/$env:APPVEYOR_JOB_ID"
   - ps: Install-Product node $env:nodejs_version
   - npm install
   - if "%nodejs_version%" == "8.11.3" (

.travis.yml

@@ -19,7 +19,7 @@ before_install:
 script:
   - 'if [ "$NODE8" = "true" ]; then npm run lint; fi'
   - 'if [ "$NODE8" = "true" ]; then npm run coverage; fi'
-  - 'if [ "$NODE8" = "true" ]; then npm run funit; fi'
+  - 'if [ "$FIREFOX" = "true" ]; then npm run funit; fi'
   - 'if [ "$NODE8" = "true" ]; then npm run test-doclint; fi'
   - 'if [ "$NODE8" = "true" ]; then npm run test-types; fi'
   - 'if [ "$NODE8" = "true" ]; then npm run bundle; fi'
@@ -32,6 +32,11 @@ jobs:
         - NODE8=true
         - FLAKINESS_DASHBOARD_NAME="Travis Chromium (node8 + linux)"
         - FLAKINESS_DASHBOARD_BUILD_URL="${TRAVIS_JOB_WEB_URL}"
+    - node_js: "8.11.3"
+      env:
+        - FIREFOX=true
+        - FLAKINESS_DASHBOARD_NAME="Travis Firefox (node8 + linux)"
+        - FLAKINESS_DASHBOARD_BUILD_URL="${TRAVIS_JOB_WEB_URL}"
     - node_js: "6.12.3"
       env:
         - NODE6=true