Ensure that the phantomjs binary has appropriate UNIX mode

[benjamn]

The 755 mode corresponds to a UNIX mode string of -rwxr-xr-x.

Closes #166.

[benjamn]

Merging with prejudice.

[zpao]

I kinda wish we instead set a max version for phantom where it didn't have this bug instead of working around an issue that will go away (and hopefully soon). We're going to forget to take that code out.

[benjamn]

@zpao we can do "~1.9.0" (which is a good idea, since right now we have >=), but I think that will still match the bad version: 1.9.1-1.

[zpao]

Well, we could match exactly here - "1.9.1" - or we could use a range - ">=1.9.0 <1.9.1-1". And when it got fixed we could switch to "~1.9.1-2" (maybe, might need to do something different there, but you can || ranges, so maybe just add || >=1.9.1-2

Full reference for version matching: https://npmjs.org/doc/json.html#dependencies

[benjamn]

Looks like we can't have || >=1.9.1-2 until that version actually exists, super lame.

[zpao]

Looks like you can do it the other way (">=1.9.1-2 || ..."), but we probably don't want to specify a version that we don't actually know works anyway :)