Update install.sh

install.sh

@@ -1,8 +1,9 @@
 #!/bin/bash
 
 # something or other about android and tmux using PREFIX
+#: "${PREFIX:=''}"
 if [ -z "$PREFIX" ]; then
-  $PREFIX=""
+  PREFIX=""
 fi
 
 # Not every platform has or needs sudo, gotta save them O(1)s