Fixing ipv6CidrBlock caps typo (#1396)

### Summary
Fixing typo

#1392 (comment)


### Related issues or links
> Include links to relevant issues or other pages.

- https://github.com/lyft/cartography/issues/...


### Checklist

Provide proof that this works (this makes reviews move faster). Please
perform one or more of the following:
- [ ] Update/add unit or integration tests.
- [ ] Include a screenshot showing what the graph looked like before and
after your changes.
- [ ] Include console log trace showing what happened before and after
your changes.

If you are changing a node or relationship:
- [ ] Update the
[schema](https://github.com/lyft/cartography/tree/master/docs/root/modules)
and
[readme](https://github.com/lyft/cartography/blob/master/docs/schema/README.md).

If you are implementing a new intel module:
- [ ] Use the NodeSchema [data
model](https://cartography-cncf.github.io/cartography/dev/writing-intel-modules.html#defining-a-node).

---------

cartography/models/aws/ec2/network_acl_rules.py

@@ -21,7 +21,7 @@ class EC2NetworkAclRuleNodeProperties(CartographyNodeProperties):
     fromport: PropertyRef = PropertyRef('FromPort')
     toport: PropertyRef = PropertyRef('ToPort')
     cidrblock: PropertyRef = PropertyRef('CidrBlock')
-    Ipv6CidrBlock: PropertyRef = PropertyRef('Ipv6CidrBlock')
+    ipv6cidrblock: PropertyRef = PropertyRef('Ipv6CidrBlock')
     egress: PropertyRef = PropertyRef('Egress')
     rulenumber: PropertyRef = PropertyRef('RuleNumber')
     ruleaction: PropertyRef = PropertyRef('RuleAction')

docs/root/modules/aws/schema.md

@@ -1332,7 +1332,7 @@ For additional explanation see https://docs.aws.amazon.com/vpc/latest/userguide/
 | fromport       | First port in the range that this rule applies to                                                                            |
 | toport         | Last port in the range that this rule applies to                                                                             |
 | cidrblock      | The IPv4 network range to allow or deny, in CIDR notation.                                                                   |
-| Ipv6CidrBlock  | The IPv6 network range to allow or deny, in CIDR notation. You must specify an IPv4 CIDR block or an IPv6 CIDR block.        |
+| ipv6cidrblock  | The IPv6 network range to allow or deny, in CIDR notation. You must specify an IPv4 CIDR block or an IPv6 CIDR block.        |
 | egress         | Indicates whether the rule is an egress rule (applied to traffic leaving the subnet).                                        |
 | rulenumber     | The rule number for the entry. ACL entries are processed in ascending order by rule number.                                  |
 | ruleaction     | Indicates whether to `allow` or `den` the traffic that matches the rule.                                                     |