Use NPM@3 and node 4.4.2 and 6

[joefitter]

• updated .travis.yml to check version of npm, install @3 if < 3
• run CI using node 4.4.2 and 6

[JoeChapman]

LGTM, @easternbloc, @daniel-ac-martin

[daniel-ac-martin]

Shouldn't we just test on node v4 (rather than 4.4.2) and v6.
i.e. The latest of each.

Does anyone know the reason for needing npm v3? (And when this dependency was introduced. - I'm guessing HOF v7.)

[JoeChapman]

Shouldn't we just test on node v4 (rather than 4.4.2) and v6.
i.e. The latest of each.

perhaps, but the current node base image uses 4.4.2

[JoeChapman]

Does anyone know the reason for needing npm v3? (And when this dependency was introduced. - I'm guessing HOF v7.)

FormidableLabs/builder#35

An update to one of the many deps (not sure which) uses postinstall, which fails now because it's dependency is not installed first

[daniel-ac-martin]

@JoeChapman: Ah okay. I forgot that this project has a Dockerfile.
Would still be nice to test against the latest v4 anf v6 though. (Do we care about v5?)

[JoeChapman]

@joefitter probably removed all bar 2 versions because travis can only run 2 builds concurrently. More version === more time spent testing/building

[daniel-ac-martin]

@JoeChapman In that case could we replace v5 with v6. That should at least catch more problems.

[JoeChapman]

@joefitter ^^

[joefitter]

Yep - happy with that

[JoeChapman]

Need to update node-sass to 3.7.0 as per sass/node-sass#1484

[joefitter]

#62