Remove zip dependency and replace with unzip equivalent (#354)

diff --git a/install-plugins.sh b/install-plugins.sh
index 8b8daee..25c12f4 100755
--- a/install-plugins.sh
+++ b/install-plugins.sh
@@ -76,7 +76,7 @@
     plugin="$1"
     jpi="$(getArchiveFilename "$plugin")"
 
-    zip -T "$jpi" >/dev/null
+    unzip -t -qq "$jpi" >/dev/null
     return $?
 }