fix regex anchoring

Author: brandonprry

msfvenom

@@ -427,7 +427,7 @@ if opts[:format] !~/ruby|rb|perl|pl|bash|sh|c|csharp|js|dll|elf/i
 end
 
 case opts[:format]
-when /ruby|rb|perl|pl|bash|^sh$|^c$|^csharp$|js_le|raw|^py/i
+when /^ruby$|^rb$|^perl$|^pl$|^bash$|^sh$|^c$|^csharp$|^js_le$|^raw$|^py$/i
 	$stdout.write Msf::Simple::Buffer.transform(payload_raw, opts[:format])
 when /asp$/
 	asp = Msf::Util::EXE.to_win32pe_asp($framework, payload_raw, exeopts)