removed instruction for .create_all_patches.sh in developerREADME

In the .developerREADME.md file, it is referred to .create_all_patches.sh to create patches for all exercises. However, it seems that this file has been removed. The .developerREADME.md should be updated accordingly. #84 (closed)

.patches/apply_patches.sh

@@ -23,7 +23,7 @@ do
   then
     echo "The solution for $exerciseName seems to be up to date."
   else
-    echo "You forgot to update the exercise or the solution for $exerciseName! Please look at the scripts `.create_all_patches.sh` or `.create_single_patch.sh` and their respective instructions to update the patches which map the exercise state to the solution state. These two shell scripts are hidden files located in the root folder of dumux-course."
+    echo "You forgot to update the exercise or the solution for $exerciseName! Please look at the script `.create_single_patch.sh` and its respective instructions to update the patches which map the exercise state to the solution state. This shell script is a hidden file located in the root folder of dumux-course."
     exit 1
   fi
 done