docs: Use present tense

script/diff

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-# No -e, because diff uses exit status 1 if differences were found.
+# No -e, because diff uses exit status 1 when differences are found.
 set -u
 
 curl -sS https://raw.githubusercontent.com/open-contracting/standard_profile_template/latest/docs/conf.py | diff -u - docs/conf.py