modified docstring for IPython/core/magics/osm.py's env class to generate better documentation

IPython/core/magics/osm.py

@@ -439,11 +439,11 b' class OSMagics(Magics):'
 
         Usage:\\
 
-          %env: lists all environment variables/values
-          %env var: get value for var
-          %env var val: set value for var
-          %env var=val: set value for var
-          %env var=$val: set value for var, using python expansion if possible
+          :%env: lists all environment variables/values
+          :%env var: get value for var
+          :%env var val: set value for var
+          :%env var=val: set value for var
+          :%env var=$val: set value for var, using python expansion if possible
         """
         if parameter_s.strip():
             split = '=' if '=' in parameter_s else ' '