method_source doesn't work with Prism

[eregon]

Because

method_source/lib/method_source/code_helpers.rb

Lines 125 to 131 in 06f21c6

	GENERIC_REGEXPS = [
	/unexpected (\$end|end-of-file|end-of-input|END_OF_FILE)/, # mri, jruby, ruby-2.0, ironruby
	/embedded document meets end of file/, # =begin
	/unterminated (quoted string|string|regexp|list) meets end of file/, # "quoted string" is ironruby
	/can't find string ".*" anywhere before EOF/, # rbx and jruby
	/missing 'end' for/, /expecting kWHEN/ # rbx
	]

and Prism uses different SyntaxError messages.

I wonder, does method_source need to filter SyntaxError messages or could it just keep adding inputs until no more SyntaxError (or EOF)?

Ref: ruby/prism#2734