Add _tag_manager partial for Google Tag Manager

As per gist from email about GTM
Merge pull request #64 from catsby/google_tag_manager

Add _tag_manager partial for Google Tag Manager
Remove Google Analytics, we now use Google Tag Manager
Permanent redirect herokuapp.com -> heroku.com, fixes #59
bump heroku to 2.40.1
Revert "Permanent redirect herokuapp.com -> heroku.com, fixes #59"

This reverts commit 63b4567bfe30e02573b6ae67d885bd1f5ef1ce59.

The client is not ready to follow this 301 just yet, see:
https://github.com/heroku/heroku/commit/5c89a16888668baa63eb7ffff8d07405f1fd6364
Change to GTM syntax
Merge pull request #66 from heroku/remove-dependency-to-ga

Change to GTM syntax
bump heroku submodule to v2.41.0
Use HTTPS everywhere
Also fix APT repos
Merge pull request #67 from heroku/brandur-https-everywhere

Use HTTPS everywhere
Bump heroku submodule to v3.0.0 tag.
Redirect non-ssl apt requests to non-ssl bucket.

Redirects from non-ssl to ssl won't be followed by apt-get, so we
should allow bare http requests to remain that way. All our packages
are signed, so there shouldn't be any danger in bare-http package
downloads; any attempts by an attacker to modify the packages would be
detected at install time.

We have users out there who are using the https URLs, so we don't want
to break those by forcing non-ssl; we should simply propagate the
sslness of the given request.
Merge branch 'allow-non-ssl-apt'

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
Document the process of publishing a new release.
bump heroku submodule to v3.0.1
Add matching braces to prevent partial execution hazards

Instigated from this blog post lamenting the practice of running
programs directly from a pipe:

  http://blog.existentialize.com/dont-pipe-to-your-shell.html

This commit comes out with greater lucidity if one uses:

  $ git diff --ignore-all-space

Also throw in a shebang.
Specify Ruby version as per buildpack suggestion.
bump heroku submodule to v3.1.0