ntfy[xmpp] trying to install dnspython3 with python2

**# pip install dnspython**
```
Requirement already satisfied: dnspython in /usr/lib/python2.7/dist-packages
```
**# pip install ntfy[xmpp]**
```
Requirement already satisfied: ntfy[xmpp] in /usr/local/lib/python2.7/dist-packages
Requirement already satisfied: requests in /usr/lib/python2.7/dist-packages (from ntfy[xmpp])
Requirement already satisfied: ruamel.yaml in /usr/local/lib/python2.7/dist-packages (from ntfy[xmpp])
Requirement already satisfied: appdirs in /usr/local/lib/python2.7/dist-packages (from ntfy[xmpp])
Collecting sleekxmpp; extra == "xmpp" (from ntfy[xmpp])
Using cached sleekxmpp-1.3.1.tar.gz
Collecting dnspython3; extra == "xmpp" (from ntfy[xmpp])
Using cached dnspython3-1.15.0.zip
Complete output from command python setup.py egg_info:
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pip-build-5wjuwe/dnspython3/setup.py", line 25
"""+"="*78, file=sys.stdout)
^
SyntaxError: invalid syntax

----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-5wjuwe/dnspython3/

```