List boolean type as "bool", which is what Skylark actually wants.

--
MOS_MIGRATED_REVID=87941912

docs/rules.md

diff --git a/docs/rules.md b/docs/rules.md
index e7092f2..081e9f9 100644
--- a/docs/rules.md
+++ b/docs/rules.md
@@ -186,7 +186,7 @@
 
 Only the following data types are allowed to pass using providers:
 
-* `boolean`
+* `bool`
 * `integer`
 * `string`
 * `file`