docs: add missing statsd to requirements

Fixes autodoc errors.

Author: jcristau

requirements/docs.in

@@ -14,6 +14,7 @@ sentry-sdk[flask]
 spec-synthase
 sqlalchemy
 sqlalchemy-migrate
+statsd
 
 sphinx
 sphinx_rtd_theme

requirements/docs.txt

@@ -1,4 +1,4 @@
-# SHA1:b4a214858c6425536b3c5f10372f4eb746eca512
+# SHA1:29bdb0ed51d27f7d78acfd07243f034b84979147
 #
 # This file is autogenerated by pip-compile-multi
 # To update, run:
@@ -1371,6 +1371,10 @@ sqlparse==0.5.3 \
     --hash=sha256:09f67787f56a0b16ecdbde1bfc7f5d9c3371ca683cfeaa8e6ff60b4807ec9272 \
     --hash=sha256:cf2196ed3418f3ba5de6af7e82c694a9fbdbfecccdfc72e281548517081f16ca
     # via sqlalchemy-migrate
+statsd==4.0.1 \
+    --hash=sha256:99763da81bfea8daf6b3d22d11aaccb01a8d0f52ea521daab37e758a4ca7d128 \
+    --hash=sha256:c2676519927f7afade3723aca9ca8ea986ef5b059556a980a867721ca69df093
+    # via -r requirements/docs.in
 swagger-spec-validator==3.0.4 \
     --hash=sha256:1a2a4f4f7076479ae7835d892dd53952ccca9414efa172c440c775cf0ac01f48 \
     --hash=sha256:637ac6d865270bfcd07df24605548e6e1f1d9c39adcfd855da37fa3fdebfed4b