Fix warning: __FILE__ in eval may not return location in binding

[yuuu]

When I used better_errors with rails-6.0.2.1 and ruby-2.7.0, I got the following warnings.

/Users/yuuu/src/github.com/fusic/mockmock-web/vendor/bundle/ruby/2.7.0/gems/better_errors-2.6.0/lib/better_errors/raised_exception.rb:40: warning: in `eval'
/Users/yuuu/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/bundler-2.1.2/libexec/bundle:46: warning: __FILE__ in eval may not return location in binding; use Binding#source_location instead

It has been modified to use Binding#source_location with reference to this issue.

pry/pry#2097

[RobinDaugherty]

Thank you @yuuu! This is a good change, but it isn't compatible with all of the versions of Ruby that we support. Can you change this use source_location only when binding responds to it, and fall back to the old behavior otherwise?

[RobinDaugherty]

Please disregard my last message, I found the time to complete this.