integrate watch into Gulp task function; rename exec argument to call

4 jobs for master in 4 minutes and 59 seconds
Status Job ID Name Coverage
  Init
passed #139931106
yarn

00:02:06

 
  Verify
failed #139931107
lint

00:01:25

passed #139931108
test

00:02:53

 
  External
passed continuous-integration/appveyor/branch

 
Name Stage Failure
failed
lint Verify
  3:17  error  'watch' is assigned a value but never used  no-unused-vars

✖ 1 problem (1 error, 0 warnings)

[04:01:24] 'lint' errored after 8.99 s
[04:01:24] Error in plugin "run-command"
Message:
Command failed: eslint
ERROR: Job failed: exit code 1