tools: update closure_linter to 2.3.17

[yosuke-furukawa]

io.js has new ES6 syntaxes like template literals.
However current closure linter can't check these ES6 syntax.

So I would like to update closure_linter to 2.3.17 (latest).
And I have already fixed some js files using make jslintfix.

[bnoordhuis]

Thanks Yosuke, landed in commits 4d8a9b1 and 85aa36d.

[bnoordhuis]

Sorry, make that 946eabd and fd30eb2. Had to amend authorship.

[shigeki]

Updating the closure linter was reverted before in 2d0011f because it needs gflags module. We need to take care of it.

~/github/io.js$ make jslint
PYTHONPATH=tools/closure_linter/ /usr/bin/python tools/closure_linter/closure_linter/gjslint.py --unix_mode --strict --nojsdoc -r lib/ -r src/ --exclude_files lib/punycode.js
Traceback (most recent call last):
  File "tools/closure_linter/closure_linter/gjslint.py", line 46, in <module>
    import gflags as flags
ImportError: No module named gflags
make: *** [jslint] Error 1