update node support to v7

[pedrotcaraujo]

I'm openning this to improve the node support to v7.

• Update engine in package.json to support Node v7.
• Update travis.yml to run env Node v7.
• Update appveyor.yml to run env Node v7.
• Update 01-installation.md adding Node v7.

It closes the issue #2559

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[googlebot]

CLAs look good, thanks!

[joscha]

cc @dignifiedquire via #2559

[dignifiedquire]

Thank you

[joscha]

Is there any way we can get a . release for this change @dignifiedquire ? Our install currently fails because of engine-strict set to true on node 7

[dignifiedquire]

I plan to do a release later tonight

[joscha]

landed in 1.5.0 - thanks @dignifiedquire