chore(dependencies): update dependency cython to v0.29.21 (#84)

renovate[bot] · renovate-bot · web-flow · commit 889ac98be205 · 2021-01-08T14:21:59.000+08:00
Co-authored-by: Renovate Bot &lt;bot@renovateapp.com&gt;
diff --git a/build-requirements.txt b/build-requirements.txt
@@ -1 +1 @@
-cython==0.29.14
+cython==0.29.21
