Upgrade and relax development dependencies
CI against ruby 2.1 as well
Fixes bug when debugger does not stops at the breakpoint set by method name

When you're setting breakpoint by method name with `break SomeClass#some_method` command,
`pry-byebug` converts it to filename and line number (line where `def some_method` statement is located). For some reason,
it does not works (`byebug` never stops at this breakpoint). Easy fix is to increment `method_object.source_location`
line number by 1 so that it points to the 1st line of the method, but it may not work properly for empty / one line methods.

It looks like you can pass method/class name instead of file name/line number to `byebug` directly which is exactly what
this PR is all about.