Pin older version of towncrier

Workaround for twisted/towncrier#346

Author: njsmith

docs-requirements.in

@@ -5,8 +5,9 @@ sphinxcontrib-trio
 # Workaround for this weird issue:
 # https://travis-ci.org/python-trio/pytest-trio/jobs/407495415
 attrs >= 17.4.0
-# != 19.9.0rc1 for https://github.com/twisted/towncrier/issues/180
-towncrier != 19.9.0rc1
+# != 19.9.0 for https://github.com/twisted/towncrier/issues/180
+# != 21.3.0 for https://github.com/twisted/towncrier/issues/346
+towncrier != 19.9.0,!= 21.3.0
 
 # pytest-trio's own dependencies
 trio >= 0.15.0

docs-requirements.txt

@@ -2,7 +2,7 @@
 # This file is autogenerated by pip-compile
 # To update, run:
 #
-#    pip-compile --output-file=docs-requirements.txt docs-requirements.in
+#    pip-compile docs-requirements.in
 #
 alabaster==0.7.12
     # via sphinx
@@ -22,12 +22,8 @@ certifi==2020.12.5
     # via requests
 chardet==4.0.0
     # via requests
-click-default-group==1.2.2
-    # via towncrier
 click==7.1.2
-    # via
-    #   click-default-group
-    #   towncrier
+    # via towncrier
 docutils==0.16
     # via
     #   sphinx
@@ -101,7 +97,7 @@ toml==0.10.2
     # via
     #   pytest
     #   towncrier
-towncrier==21.3.0
+towncrier==19.2.0
     # via -r docs-requirements.in
 trio==0.18.0
     # via -r docs-requirements.in