Add citizenlab namespace alias to stix files

[dandye]

The stix files fail stix validation[1] because they are missing an alias for the namespace. This PR adds that missing namespace alias.

Each file was modified with:

sed -i.bak 's/=":/="citizenlab:/g'  ./201712_Cyberbit/stix.xml
sed -i.bak 's|xmlns:="https|xmlns:citizenlab="https|' ./201712_Cyberbit/stix.xml

Before

 stix-validator.py ./201712_Cyberbit/stix.xml
[-] Performing xml schema validation on ./201712_Cyberbit/stix.xml
[-] Unexpected error occurred with file './201712_Cyberbit/stix.xml'. No further validation will be performed: Failed to parse QName 'xmlns:', line 29, column 8 (stix.xml, line 29)
================================================================================
[-] Results: ./201712_Cyberbit/stix.xml
[!] Fatal Error: Failed to parse QName 'xmlns:', line 29, column 8 (stix.xml, line 29)

After

stix-validator.py ./201712_Cyberbit/stix.xml
[-] Performing xml schema validation on ./201712_Cyberbit/stix.xml
================================================================================
[-] Results: ./201712_Cyberbit/stix.xml
[+] XML Schema: True

[1] https://github.com/STIXProject/stix-validator