Update comments in genrule.go.

Test: Noop
Change-Id: Ib341899ea0f04e059d5471ee6e5bff8ebba82583
diff --git a/android/paths.go b/android/paths.go
index a62c9e3..b7117a3 100644
--- a/android/paths.go
+++ b/android/paths.go
@@ -665,7 +665,7 @@
 	return Paths(ret)
 }
 
-// WritablePaths is a slice of WritablePaths, used for multiple outputs.
+// WritablePaths is a slice of WritablePath, used for multiple outputs.
 type WritablePaths []WritablePath
 
 // Strings returns the string forms of the writable paths.