Update binding.gyp

[egasimus]

Node 14.17.5, pnpm 6.14.3, both installed via Nix 2.3.15 on Ubuntu 20.04: node-gyp fails, returning a big pile of warnings, plus this one error:

│ ../src/./tree_sitter_markdown/block_context.cc: In member function ‘tree_sitter_markdown::ParseState tree_sitter_markdown::Bloc                                                                                                                                      
│ ../src/scanner.cc:9:72: error: exception handling disabled, use ‘-fexceptions’ to enable                                                                                                                                                                             
│     9 | #define TREE_SITTER_MARKDOWN_ASSERT(condition) if (!(condition)) throw 1;   

With the attached fix, the build succeeds and tree-sitter-markdown seems to work normally so far.

Based on info from nodejs/node-gyp#17

[VincentCordobes]

What's the difference with #34 ?