Move require outside of class method

Otherwise if m is installed via gem install and run in a repo that doesn't have 
it inside of its Gemfile, the following error is thrown: 

cannot load such file -- method_source (LoadError)

All props on solving this in light of my derping around go to @schneems.

lib/m/test_method.rb

@@ -1,3 +1,5 @@
+require "method_source"
+
 module M
   ### Simple data structure for what a test method contains.
   #
@@ -22,7 +24,7 @@ def self.create(suite_class, test_method)
       #
       # The end line should be the number of line breaks in the method source,
       # added to the starting line and subtracted by one.
-      require "method_source"
+
       end_line = method.source.split("\n").size + start_line - 1
 
       # Shove the given attributes into a new databag