Switch ruby styleguide to recommend 'fat arrow' hash syntax

I think the fat arrow (a.k.a. hash rocket) hash syntax is better than the new 1.9 hash syntax

```ruby
#bad
hash = {foo: :bar}

#good
hash = {:foo => :bar}
```

My reasoning is as follows:

The new 1.9 syntax can only be used for hashes with Symbol literals as the keys.  All other usage has to use the fat arrow syntax.

```ruby
variable = :foo
hash = {symbol: 1, "string" => 2, 42 => 3, true => 4, variable => 5}
# => {:symbol=>1, "string"=>2, 42=>3, true=>4, :foo=>5}
```
Note: `Hash#inspect` uses the fat arrow syntax.

The 1.9 syntax cannot be used if the symbol name matches a ruby keyword.  e.g.:

```ruby
# This will cause a syntax error because if is a keyword
validates :password, presence: { if: :password_required? }, confirmation: true
```

It introduces a second way of writing symbols, which makes it harder to read.  Compare the above validates example with:

```ruby
validates :password, :presence => { :if => :password_required? }, :confirmation => true
```

In general, the fat arrow syntax is much more consistent than the new 1.9 syntax.


I haven't really seen a reasoned argument for using the 1.9 syntax.


Another opinion: http://www.michaelxavier.net/posts/2011-07-01-I-Dont-Understand-The-New-Ruby-Hash-Syntax.html