fix: make docs output deterministic

docs/BUILD.bazel

diff --git a/docs/BUILD.bazel b/docs/BUILD.bazel
index b07454f..8454806 100644
--- a/docs/BUILD.bazel
+++ b/docs/BUILD.bazel
@@ -9,11 +9,22 @@
 
 genrule(
     name = "docgen",
-    outs = ["gen/" + d for d in _DOCS],
-    cmd = "$(execpath //cmd/docgen) $(@D)/gen",
+    outs = ["raw/" + d for d in _DOCS],
+    cmd = "$(execpath //cmd/docgen) $(@D)/raw",
     tools = ["//cmd/docgen"],
 )
 
+# Make a deterministic output by stripping date info
+[
+    genrule(
+        name = "strip_date_%s" % src,
+        srcs = ["raw/" + src],
+        outs = ["gen/" + src],
+        cmd = "sed 's#by spf13/cobra on .*#by spf13/cobra#' <$< >$@",
+    )
+    for src in _DOCS
+]
+
 # Help developers who get a red CI result by telling them how to fix it
 _failure_message = "\nPlease update the docs by running\n    bazel run //docs:update"
 

docs/aspect.md

diff --git a/docs/aspect.md b/docs/aspect.md
index 15fea1a..8043d67 100644
--- a/docs/aspect.md
+++ b/docs/aspect.md
@@ -18,4 +18,4 @@
 
 * [aspect version](aspect_version.md)	 - Print the version of aspect CLI as well as tools it invokes
 
-###### Auto generated by spf13/cobra on 4-Sep-2021
+###### Auto generated by spf13/cobra

docs/aspect_version.md

diff --git a/docs/aspect_version.md b/docs/aspect_version.md
index 78e9616..7e3c086 100644
--- a/docs/aspect_version.md
+++ b/docs/aspect_version.md
@@ -28,4 +28,4 @@
 
 * [aspect](aspect.md)	 - Aspect.build bazel wrapper
 
-###### Auto generated by spf13/cobra on 4-Sep-2021
+###### Auto generated by spf13/cobra