fix(build): fix variable in build script (#237)

diff --git a/build.sh b/build.sh
index 6b0407e..3f552a8 100755
--- a/build.sh
+++ b/build.sh
@@ -170,7 +170,7 @@
     exit 1
   fi
 
-  libevent_dir=$(ls | grep libevent | grep .*[^zip]$)
+  libevent_dir=$(ls | grep libevent | grep .*[^zip^txt]$)
   cd ${libevent_dir}
   if [ $? -ne 0 ]; then
     exit 1