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
Fix indentation in keywords
Update Travis CI build to install gperf.
Merge pull request #1037 from carsonmcdonald/traviscigperf

Update Travis CI build to install gperf
Merge pull request #1036 from kano4/pr-fix-indentation-in-keywords

Fix indentation in keywords
update lex.def
remove gperf installation that is not needed if src/lex.def is properly updated; cancel #1037
bugfix escape charactor for Regexp class
Merge pull request #1038 from kouki-o-iij/pr-regexp-escape

bugfix escape charactor for Regexp class