Fix wrong number of arguments in `Array#fetch`; fix
MODIFY
mrbgems/mruby-array-ext/mrblib/array.rb
mrbgems/mruby-array-ext/mrblib/array.rb
@@ -291,7 +291,7 @@ class Array
# #=> "100 is out of bounds"
#
- def fetch(n=nil, ifnone=NONE, &block)
+ def fetch(n, ifnone=NONE, &block)
warn "block supersedes default value argument" if !n.nil? && ifnone != NONE && block
idx = n

Fix wrong number of arguments in `Array#fetch`; fix #4170