Pager: use the `::jruby?` helper from BaseHelpers
Method: fix indentation of private methods
Method: shorten helper method calls

`BaseHelpers` module is already included.
Do not recommend to install pry-doc in some cases

There is no sense to install "pry-doc" on Ruby platforms other than MRI,
since "pry-doc" is for MRI only. Although "pry-doc" works on non-MRI
platforms, it still shows C source code. Haha.