Fix case sensitivity in KV.get

[zerowidth]

This PR fixes a bug reported internally:

[1] pry(main)> GitHub.kv.set("foo", "bar")
=> nil
[2] pry(main)> GitHub.kv.set("Foo", "baz")
=> nil
[3] pry(main)> GitHub.kv.get("foo")
=> #<GitHub::Result:0xd41c value: "baz">

The expected behavior was that foo and Foo would be treated as different keys. However, the MySQL default utf8 collation is case insensitive. This changes the fetch code to be case-insensitive to match the default MySQL behavior:

Before:

set "foo", "lower"
get "foo" # => "lower"
get "FOO" # => nil
set "FOO", "upper" # overwrites existing 'foo' key
get "foo" # => "upper", matching based on original key name
get "FOO" # => nil, since ruby "FOO" string doesn't match the "foo" key returned from the database

After:

set "foo", "lower"
get "foo" # => "lower"
get "FOO" # => "lower"
set "FOO", "upper"
get "foo" # => "upper"
get "FOO" # => "upper"

This doesn't help if you're expecting case sensitivity, but it makes the set/get behavior consistent.

[jshorty]

Thanks for fixing this! New to this codebase but given the default MySQL behavior, coercing to all-downcase keys outside of the query makes sense to me here.

[zerowidth]

Released as 0.5.2.