update build_config.rb
add mruby-enum-ext
add Enumerable#drop
add Enumerable#drop_while
add Enumerable#take, Enumerable#take_while
fix spelling
fix comment
Add gem version to build summary if it exists.
Merge pull request #1034 from skandhas/pr-add-mruby-enumerable-ext

add mrbgem: mruby-enum-ext and some methods.
Merge pull request #1035 from carsonmcdonald/printgemver

Add gem version to build summary