Fixed `mnc` encoding

According to 3GPP TS 24.008 section 10.5.5.36 PLMN identity of the CN operator

Change-Id: I400435abfa8b67da886fc39c801e1abba39725bf
diff --git a/pySim/utils.py b/pySim/utils.py
index c25560c..735468e 100644
--- a/pySim/utils.py
+++ b/pySim/utils.py
@@ -413,7 +413,7 @@
     if len(mnc) == 0:
         mnc = "FFF"
     elif len(mnc) == 1:
-        mnc = "F0" + mnc
+        mnc = "0" + mnc + "F"
     elif len(mnc) == 2:
         mnc += "F"