fix(build): Build without xrm

When xrm was disabled, main.cpp was missing the complete defintion of
connection from connection.hpp, which was included xresources.hpp when
xrm was enabled.

src/main.cpp

@@ -6,6 +6,7 @@
 #include "utils/env.hpp"
 #include "utils/inotify.hpp"
 #include "utils/process.hpp"
+#include "x11/connection.hpp"
 
 using namespace polybar;