fix(capslock_x11): properly release the X display handle

This fixes caps lock detection after a while, and removes the "Maximum
number of clients reached" message on stdout.

src/platform/capslock_x11.cpp

@@ -35,6 +35,7 @@ bool Platform::capsLockEnabled()
         unsigned n;
         XkbGetIndicatorState(d, XkbUseCoreKbd, &n);
         caps_state = (n & 0x01) == 1;
+        XCloseDisplay(d);
     }
     return caps_state;
 }