Fix run-editor bug with cmd2 >= 2.0.0 compatibility

In cmd2, the upstream authors decided to rename a method in 2.0.0
without providing a backwards compatibility wrapper.  Let's add that
locally.

Change-Id: Iaa17b93db13ba330551799cce5f0388c78217224
Closes: OS#6071
diff --git a/pySim-shell.py b/pySim-shell.py
index f6cd75d..9897d29 100755
--- a/pySim-shell.py
+++ b/pySim-shell.py
@@ -17,7 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from typing import List
+from typing import List, Optional
 
 import json
 import traceback
@@ -144,7 +144,18 @@
     return rs, card
 
 
-class PysimApp(cmd2.Cmd):
+class Cmd2Compat(cmd2.Cmd):
+    """Backwards-compatibility wrapper around cmd2.Cmd to support older and newer
+    releases. See https://github.com/python-cmd2/cmd2/blob/master/CHANGELOG.md"""
+    def run_editor(self, file_path: Optional[str] = None) -> None:
+        if version.parse(cmd2.__version__) < version.parse("2.0.0"):
+            # pylint: disable=no-member
+            return self._run_editor(file_path)
+        else:
+            # pylint: disable=no-member
+            return super().run_editor(file_path)
+
+class PysimApp(Cmd2Compat):
     CUSTOM_CATEGORY = 'pySim Commands'
 
     def __init__(self, card, rs, sl, ch, script=None):
diff --git a/pySim/filesystem.py b/pySim/filesystem.py
index b5d0ccd..04e849b 100644
--- a/pySim/filesystem.py
+++ b/pySim/filesystem.py
@@ -649,7 +649,7 @@
                 with open(filename, 'w') as text_file:
                     json.dump(orig_json, text_file, indent=4)
                 # run a text editor
-                self._cmd._run_editor(filename)
+                self._cmd.run_editor(filename)
                 with open(filename, 'r') as text_file:
                     edited_json = json.load(text_file)
                 if edited_json == orig_json:
@@ -917,7 +917,7 @@
                 with open(filename, 'w') as text_file:
                     json.dump(orig_json, text_file, indent=4)
                 # run a text editor
-                self._cmd._run_editor(filename)
+                self._cmd.run_editor(filename)
                 with open(filename, 'r') as text_file:
                     edited_json = json.load(text_file)
                 if edited_json == orig_json: