Replace gulp-sass with gulp-ruby-sass

This changeset attempts to resolve #117 by replacing `gulp-sass`
(`libsass`) with `gulp-ruby-sass` (Ruby Sass). The main tradeoffs are that
Ruby Sass can be slower than `libsass` and requires the Ruby runtime,
but Ruby Sass also appears to be more stable, doesn't require the Node
bindings for `libsass`, and has all of the Sass features.

Arbitrary data points around build durations:

**gulp-ruby-sass**

```
./scripts/npm.sh run build-debug  1.29s user 0.27s system 30% cpu 5.042 total
./scripts/npm.sh run build-debug  1.28s user 0.27s system 31% cpu 4.957 total
./scripts/npm.sh run build-debug  1.29s user 0.27s system 31% cpu 4.955 total
```

**gulp-sass**

```
./scripts/npm.sh run build-debug  1.42s user 0.31s system 32% cpu 5.394 total
./scripts/npm.sh run build-debug  1.39s user 0.30s system 31% cpu 5.370 total
./scripts/npm.sh run build-debug  1.39s user 0.30s system 32% cpu 5.155 total
```

Sass test file:

```scss
$font-stack:    Helvetica, sans-serif;
$primary-color: #333;

body {
  font: 100% $font-stack;
  color: $primary-color;
}
```

I assume that as the amount of Sass piles up, the performance benefits
of `gulp-sass` would breakthrough. Not sure though.
Switch from npm module to calling npm directly

A new npm package, `gulp-ruby-sass`, was added in 7de060d.
The npm ansible module appears to not have picked up this up, and
`gulp-ruby-sass` was not installed.

Switching to calling `npm install` directly did install the package.
Add NPM shrinkwrap file

This helps lockdown the versions of a package's dependencies so that
we can control which versions of each dependency will be used when
`npm install` is run.
v8flags consistently failing clean VAGRANT_ENV="TEST" provisions

Reverting to v1.0.1 resolved the issues. v8flags `CHANGELOG` below:

  2014-09-03 - v1.0.0 - first major version release
  2014-11-17 - v1.0.2 - get node executable from process.env._
  2014-11-17 - v1.0.3 - get node executable during npm install via
                        process.env.NODE
  2014-11-18 - v1.0.4 - wrap node executable path in quotes
  2014-11-26 - v1.0.5 - get node executable from process.execPath
  2014-12-09 - v1.0.6 - revert to 1.0.0 behavior
Merge branch 'feature/hmc/gulp-ruby-sass' into develop