changed the enviroment variable from BUTTON to BLOCK_BUTTON to make the script i use in i3 work

dwmblocks.c

@@ -70,10 +70,10 @@ void getcmd(const Block *block, char *output)
 	FILE *cmdf;
 	if (*button)
 	{
-		setenv("button", button, 1);
+		setenv("BLOCK_BUTTON", button, 1);
 		cmdf = popen(cmd, "r");
 		*button = '\0';
-		unsetenv("BUTTON");
+		unsetenv("BLOCK_BUTTON");
 	}
 	else
 	{