Fix a typo in syntax-extensions.rst
Fix a typo in syntax-extensions.rst

Zimmi48/coq,coq/coq,SkySkimmer/coq,coq/coq,ejgallego/coq,Zimmi48/coq,ejgallego/coq,coq/coq,SkySkimmer/coq,Zimmi48/coq,SkySkimmer/coq,Zimmi48/coq,SkySkimmer/coq,coq/coq,ejgallego/coq,ejgallego/coq