ci(travis): set dist: trusty in .travis.yml (#777)

to avoid errored Travis CI build on Node.js 12

including NOTE with a TODO item

.travis.yml

@@ -1,5 +1,10 @@
 sudo: false
 
+# NOTE: dist is added here to ensure that Travis CI works consistently
+# on Node.js 12. It is desired to remove it once this issue is resolved
+# or otherwise goes away.
+dist: trusty
+
 env:
   global:
     - ANDROID_API_LEVEL=28