Remove `Time` defined check in test.
Merge pull request #2207 from take-cheeze/time_def

Remove `Time` defined check in mruby-time gem test.
Make Array#[]= raise IndexError.

If second param is negative, Array#[] raise IndexError.
Replace from include <>, to include "".
Merge pull request #2208 from yui-knk/array-error

Make Array#[]= raise IndexError.
Merge pull request #2209 from yui-knk/fix-include

Replace from include <>, to include "".