update dev install instruction

Author: oscarwumit

documentation/source/users/rmg/installation/anacondaDeveloper.rst

@@ -110,9 +110,9 @@ Installation by Source Using Anaconda Environment for Unix-based Systems: Linux
 
     conda activate rmg_env
 
-#. Switch the conda solver to libmamba again, to accelerate any changes you might make to this conda environment in the future::
+#. Switch the conda solver back to default, to avoid potential conflicts with Julia commands below::
 
-    conda config --set solver libmamba
+    conda config --set solver classic
 
 #. Compile RMG-Py after activating the conda environment ::