Allow Node to use more memory for old space

This flag essentially configures how much memory Node can use. If it’s too low, then Node processes may hang as Node spends time garbage collecting. Increasing it allows more memory to be used before garbage collection is necessary.  Travis VMs have 7.5GB of memory, so set the limit to just below that to avoid running out of memory completely.

.travis.yml

@@ -7,11 +7,12 @@ node_js:
 - 8
 env:
   global:
+  - CHROMEDRIVER_VERSION=LATEST
   - NODE_ENV=production
-  - SMOKE_URL=https://llk.github.io/scratch-gui/$TRAVIS_PULL_REQUEST_BRANCH
+  - NODE_OPTIONS=--max-old-space-size=7250
   - NPM_TAG=latest
   - RELEASE_VERSION="0.1.0-prerelease.$(date +'%Y%m%d%H%M%S')"
-  - CHROMEDRIVER_VERSION=LATEST
+  - SMOKE_URL=https://llk.github.io/scratch-gui/$TRAVIS_PULL_REQUEST_BRANCH
 cache:
   directories:
   - node_modules