Fix small typo in documentation

Signed-off-by: Stefan Weil <sw@weilnetz.de>

Author: stweil

README.md

@@ -3,7 +3,7 @@
  PHP Static Analysis in Github Actions. 
  ======================================
 
-PHPStan finds bugs in your code without writing tests by using runnin static analysis on your project's code.
+PHPStan finds bugs in your code without writing tests by using running static analysis on your project's code.
 
 Usage
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