Broken links to source code in wiki

The link URLs to GHC source code are incorrect.

For example, the following path in the pages:

• https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/parser

  • compiler/parser/Lexer.x links to /trac/ghc/browser/ghc/compiler/parser/Lexer.x

• https://gitlab.haskell.org/ghc/ghc/wikis/commentary/rts/storage/heap-objects

  • Closures.h links to /trac/ghc/browser/includes/rts/storage/Closures.h