Fix failing npm lint script

[rappestad]

I cloned this repository to work on #600, but got the error below. The change in this pull request lets me run the test suite via Docker. With this out of the way, I could not reproduce the problem described in #600; that test passed with node 8 as well as node 10.

My developer console:

> docker build -t monument .
...
> docker run monument

Container output:

2018-10-03T20:34:55.795062900Z 
> monument@5.3.0 test /src
> npm run lint && nyc ava -s *.test.js utils/**/*.test.js web-sockets/**/*.test.js security/**/*.test.js routes/**/*.test.js
2018-10-03T20:34:55.795113500Z 
2018-10-03T20:34:56.009310600Z 
> monument@5.3.0 lint /src
> bin/lint.js
2018-10-03T20:34:56.009360500Z 
/usr/bin/env: node : No such file or directory
npm ERR! file sh
npm ERR! code ELIFECYCLE
npm ERR! errno ENOENT
npm ERR! syscall spawn
npm ERR! monument@5.3.0 lint: `bin/lint.js`
npm ERR! spawn ENOENT
npm ERR! 
npm ERR! Failed at the monument@5.3.0 lint script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
2018-10-03T20:34:56.033124500Z 
npm ERR! A complete log of this run can be found in:
npm ERR!     /root/.npm/_logs/2018-10-03T20_34_56_027Z-debug.log
npm ERR! Test failed.  See above for more details.

[coveralls]

Coverage remained the same at 98.218% when pulling e87681606011d8c5a9bfbb953704e91d4d0d9451 on rappestad:master into 9cc92f3589175e5329904d1a5743424ee3e278d7 on ansble:master.

[designfrontier]

Thanks!