Fix for warning: deprecated conversion from string constant to 'char*'

--- src/blackbox.cc.orig	Tue Oct 18 13:33:25 2005
+++ src/blackbox.cc	Tue Apr 25 16:44:10 2017
@@ -36,6 +36,7 @@
 #include <sys/stat.h>
 #include <assert.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <unistd.h>
 
 // #define FOCUS_DEBUG
@@ -75,7 +76,7 @@ void Blackbox::reload_rc(void) {
 
 
 void Blackbox::init_icccm(void) {
-  char* atoms[7] = {
+  const char* atoms[7] = {
     "WM_COLORMAP_WINDOWS",
     "WM_PROTOCOLS",
     "WM_STATE",
@@ -85,7 +86,7 @@ void Blackbox::init_icccm(void) {
     "_MOTIF_WM_HINTS"
   };
   Atom atoms_return[7];
-  XInternAtoms(XDisplay(), atoms, 7, false, atoms_return);
+  XInternAtoms(XDisplay(), (char **)atoms, 7, false, atoms_return);
   xa_wm_colormap_windows = atoms_return[0];
   xa_wm_protocols = atoms_return[1];
   xa_wm_state = atoms_return[2];