* Update reline-0.5.7

* Update irb-1.13.1

(https://github.com/ruby/irb/pull/807)

https://github.com/ruby/irb/commit/2cccc448de

* Remove trailing spaces

* Migrate show_source tests to integration tests

Because show_source tests often need to define class and/or methods,
they can easily leak state to other tests. Changing them to integration
tests will ensure that they are run in a clean environment.

* Fix NoMethodError caused by SourceFinder#method_target

https://github.com/ruby/irb/commit/3c39f13397c72a8db24e50afdcb8942e6c4ea12f

want to access a methods origin definition.  It allows for chaining
of multiple esses to further go up the classes as needed.
(https://github.com/ruby/irb/pull/770)

https://github.com/ruby/irb/commit/eec1329d5a

(https://github.com/ruby/irb/pull/684)

After this change, `RubyLex` will not interact with `Context` directly
in any way. This decoupling has a few benefits:

- It makes `RubyLex` easier to test as it no longer has a dependency on
  `Context`. We can see this from the removal of `build_context` from
  `test_ruby_lex.rb`.
- It will make `RubyLex` easier to understand as it will not be affected
  by state changes in `Context` objects.
- It allows `RubyLex` to be used in places where `Context` is not available.

https://github.com/ruby/irb/commit/d5b262a076

(https://github.com/ruby/irb/pull/658)

* Decouple `edit` command from `show_source`

2 commands should not depend on each other. If `edit` command also needs
to find a source, the source finding logic should be extracted into a
separate class.

* Return nil if is not an actual file path

* Refactor SourceFinder

https://github.com/ruby/irb/commit/9790517a0c