changed the install-plumed action author

Author: Iximiel

.github/workflows/main.yml

@@ -46,7 +46,7 @@ jobs:
         ccache -s
         mkdir -p ~/.ccache/ccache
     - name: Install plumed
-      uses: Iximiel/install-plumed@v1
+      uses: plumed/install-plumed@v1
       with:
         CC: "ccache mpicc"
         CXX: "ccache mpic++"