fix wp link

Author: Lucien Grondin

mathics/core/parser/README.md

@@ -4,8 +4,7 @@
 
 The Mathics parser is an operator precedence parser that implements
 the precedence climbing method. The AST (Abstract Syntax
-Tree) produced after parsing is a kind of [M-expression](M-expression
-<https://en.wikipedia.org/wiki/M-expression) which is then used in
+Tree) produced after parsing is a kind of [M-expression](https://en.wikipedia.org/wiki/M-expression) which is then used in
 evaluation.
 
 The Wolfram language is surprisingly complex and has quite a few subtleties;