Fixed the URL for PL/0

Author: yhirose

README.md

@@ -399,7 +399,7 @@ Sample codes
   * [Calculator (with parser operators)](https://github.com/yhirose/cpp-peglib/blob/master/example/calc2.cc)
   * [Calculator (AST version)](https://github.com/yhirose/cpp-peglib/blob/master/example/calc3.cc)
   * [PEG syntax Lint utility](https://github.com/yhirose/cpp-peglib/blob/master/lint/peglint.cc)
-  * [PL/0 Interpreter](https://github.com/yhirose/cpp-peglib/blob/master/language/pl0/pl0.cc)
+  * [PL/0 Interpreter](https://github.com/yhirose/cpp-peglib/blob/master/pl0/pl0.cc)
 
 Tested compilers
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