gitignore: Fix subprojects

Change-Id: Ib60275837c28eaa7d4f2d9da0181ea63f8a23d17
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/.gitignore b/.gitignore
index 327ea97..be43dc8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 /build*/
-/subprojects/*/
+/subprojects/*
+!/subprojects/fmt.wrap
+!/subprojects/googletest.wrap