Exclude "asterix-app/src/test/resources/externallib/" in .gitignore.

Change-Id: Ib1af6dd556009321d0803ffdf9916146e866bb87
Reviewed-on: https://asterix-gerrit.ics.uci.edu/654
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Till Westmann <tillw@apache.org>
diff --git a/.gitignore b/.gitignore
index d6ab1f1..f8e0b2d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,7 @@
 asterix_logs
 build
 bin
+asterix-app/src/test/resources/externallib/
 asterix-app/rttest/
 asterix-app/mdtest/
 asterix-app/opttest/