Endless loop when running `lektor server`

[zerok]

✗ pip list
Package         Version      Location
--------------- ------------ -------------------------------------------------------------
argh            0.26.2
asn1crypto      0.22.0
aspy.yaml       0.3.0
Babel           2.4.0
cached-property 1.3.0
cffi            1.10.0
click           6.7
cryptography    1.8.1
ExifRead        2.1.2
Fabric3         1.13.1.post1
first           2.0.1
Flask           0.12.1
idna            2.5
inifile         0.3
itsdangerous    0.24
Jinja2          2.9.6
Lektor          3.0          /Users/zerok/src/github.com/ulope/pyformat.info/vendor/lektor
MarkupSafe      1.0
mistune         0.7.4
nodeenv         1.1.2
packaging       16.8
paramiko        2.1.2
pathtools       0.1.2
pip             10.0.1
pip-tools       2.0.2
pre-commit      0.13.6
py              1.4.33
pyasn1          0.2.3
pycparser       2.17
pyOpenSSL       17.0.0
pyparsing       2.2.0
pytest          3.0.7
pytz            2017.2
PyYAML          3.12
requests        2.14.2
setuptools      39.2.0
six             1.10.0
virtualenv      15.1.0
watchdog        0.8.3
Werkzeug        0.12.1
wheel           0.31.1


✗ lektor server
/Users/zerok/.local/share/virtualenvs/pyformat.info-fzSP8oiJ/bin/../lib/python3.6/site.py:165: DeprecationWarning: 'U' mode is deprecated
  f = open(fullname, "rU")
/Users/zerok/Library/Caches/Lektor/packages/1144362b6b722bad22af2cd37b25af64/pygments/util.py:27: DeprecationWarning: Flags not at the start of the expression '<(.+?)(\\s.*?)?>.*?</' (truncated)
  tag_re = re.compile(r'<(.+?)(\s.*?)?>.*?</.+?>(?uism)')
 * Project path: /Users/zerok/src/github.com/ulope/pyformat.info/pyformat.info.lektorproject
 * Output path: /Users/zerok/Library/Caches/Lektor/builds/136ab102556fc537fdfb3e3d8a08da0d
Started source info update
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
Finished source info update in 0.10 sec
Started build
Finished build in 0.08 sec
Started prune
Finished prune in 0.01 sec
Started build
Finished build in 0.09 sec
Started prune
Finished prune in 0.01 sec
Started build
Finished build in 0.08 sec
Started prune
Finished prune in 0.02 sec
Started build
Finished build in 0.09 sec
Started prune
Finished prune in 0.01 sec
...

I'll try tomorrow if updating the dependencies helps.