[Suggestion] Do not throw error on string.dump

[tooolbox]

• GopherLua is a Lua5.1 implementation. You should be familiar with Lua programming language. Have you read Lua 5.1 reference manual carefully?
• GopherLua is a Lua5.1 implementation. In Lua, to keep it simple, it is more important to remove functionalities rather than to add functionalities unlike other languages . If you are going to introduce some new cool functionalities into the GopherLua code base and the functionalities can be implemented by existing APIs, It should be implemented as a library.

Please answer the following before submitting your issue:

1. What version of GopherLua are you using? : Roughly 8bfc767
2. What version of Go are you using? : 1.14 I believe
3. What operating system and processor architecture are you using? : Windows x86
4. What did you do? : Tried to load compat52 or compat53 in gopher-lua
5. What did you expect to see? : Success
6. What did you see instead? : The error about gopher-lua not supporting string.dump

The compat52 and compat53 libraries test for LuaJIT by checking the output of string.dump, as you can see here. By throwing an error on the use of string.dump, you effectively bar the use of (unmodified) compat libraries. Perhaps it would be better to return nil?

[tooolbox]

Any feedback @yuin ?