Fix typo in a comment

dune/fufem/test/dunepythontest.cc

@@ -22,7 +22,7 @@ int main(int argc, char** argv) try
     Python::start();
 
 
-    // You will normally want to exucute code in the context of the main
+    // You will normally want to execute code in the context of the main
     // module denoted __main__ inside of python.  For using other modules
     // see below.
     auto pyMain = Python::main();