Fixes Homebrew/homebrew#30046.

rcov is not compatible with Ruby 2.0.

The areas that we are interested in optimizing for performance are
things that are invoked repeatedly, and are not evident in the test
suite.

It is not a hotspot and causes an ordering dependency in the tests.

Closes Homebrew/homebrew#30017.

Ruby 2.2's native Pathname#/ accepts only string-like objects.

Pathname#inspect on Ruby 2.0 throws away the encoding of the object's
underlying string and returns a string tagged as ASCII-8BIT.

If you simply write

  puts Pathname.new("some string with non-ascii bytes").inspect

no error will be raised, because the implementation of Pathname#inspect
does not call into Object#inspect.

However, if you wrap that pathname object in an array first, then

  puts [Pathname.new("some string with non-ascii bytes")].inspect

will raise Encoding::CompatibilityError: "inspected result must be ASCII
only or use the same encoding with default external".

Raising an error in this codepath is new in Ruby 2.0, and this specific
bug is fixed in Ruby 2.1. I've opened a bug upstream:
  https://bugs.ruby-lang.org/issues/9915

Fixes Homebrew/homebrew#29947.

Closes Homebrew/homebrew#29880.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>