Update ruby version for manual installation to 2.1.2

**What does this MR do?**

Updates ruby version from 2.0 to 2.1.2

**Why was this MR needed?**

GitLab dropped support for ruby 1.9.3 and recommends 2.1 therefore docs need update.

**What are the relevant issue numbers?**

#360, #362

/cc @sytse

Mention merge marshalls

What do you think about people mentioning you @jeroenvanbaarsen and @dblessing ?

Remove secondary user email

Fixes #1286

Spell out rake tasks for omnibus-gitlab

Fix go meta tag

See https://github.com/gitlabhq/gitlabhq/pull/5958#issuecomment-45397555

Patch `rake cache:clear` for large amounts of keys

More swap is also an option

Redirect after login

Use html5 tags for better semantic

MR diff loading spinner

When you click `Changes` tab if diff is big - you now see loading spinner

Ui improvements

Skip to buttons on tabbing in issues page

This will skip tabbing right to "Add comment" or "close" buttons.

http://www.w3.org/TR/html5/editing.html#sequential-focus-navigation-and-the-tabindex-attribute

For tabindex:

```
If the value is a negative integer
The user agent must set the element's tabindex focus flag, but should not allow the element to be reached using sequential focus navigation.
```

Remove observers from application

Part of #1133

Regression issue on rc

Fixes #7163, copy init script while upgrading (master branch)

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix permissions

Fixes #1358

Mention all update guides in monthly release doc

Fixes #1328

If user was a member of both group and project and group access level
was higher it was not respected and user got lowest project access
level. Now it is fixed and user get highest access level
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Create 6.0-to-7.0 update guide

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix 500 error when transfer project from admin area

Fixes #1349

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>