euicc: Fix TLV IE definitions for SetNickname{Req,Resp}

The metaclass uese the 'nested' attribute, while the existing code
accidentially used the 'children' attribute.  The latter is used
by instances for actual child classes, while the Class/nested
attribute is for the list of classes whose instancse could be potential
children.

Change-Id: I968bd84d074dcdcec37d99be5d3d4edac9c35a0c
diff --git a/pySim/euicc.py b/pySim/euicc.py
index c070525..19b1c57 100644
--- a/pySim/euicc.py
+++ b/pySim/euicc.py
@@ -245,11 +245,11 @@
 # SGP.22 Section 5.7.21: ES10c SetNickname
 class SnrProfileNickname(BER_TLV_IE, tag=0x8f):
     _construct = Utf8Adapter(GreedyBytes)
-class SetNicknameReq(BER_TLV_IE, tag=0xbf29, children=[Iccid, SnrProfileNickname]):
+class SetNicknameReq(BER_TLV_IE, tag=0xbf29, nested=[Iccid, SnrProfileNickname]):
     pass
 class SetNicknameResult(BER_TLV_IE, tag=0x80):
     _construct = Enum(Int8ub, ok=0, iccidNotFound=1, undefinedError=127)
-class SetNicknameResp(BER_TLV_IE, tag=0xbf29, children=[SetNicknameResult]):
+class SetNicknameResp(BER_TLV_IE, tag=0xbf29, nested=[SetNicknameResult]):
     pass
 
 # SGP.32 Section 5.9.10: ES10b: GetCerts