dwm can't be build / missing BROWSER define

[mxraw]

The fix for #191 causes dwm to not compile anymore due to usage of undefined BROWSER define.

$ make
dwm build options:
CFLAGS   = -std=c99 -pedantic -Wall -Wno-deprecated-declarations -Os -I/usr/X11R6/include -I/usr/include/freetype2 -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_POSIX_C_SOURCE=200809L -DVERSION="6.2" -DXINERAMA
LDFLAGS  = -L/usr/X11R6/lib -lX11 -lXinerama -lfontconfig -lXft -lX11-xcb -lxcb -lxcb-res
CC       = cc
cc -c -std=c99 -pedantic -Wall -Wno-deprecated-declarations -Os -I/usr/X11R6/include -I/usr/include/freetype2 -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_POSIX_C_SOURCE=200809L -DVERSION=\"6.2\" -DXINERAMA dwm.c
In file included from dwm.c:333:
config.h:163:96: error: ‘BROWSER’ undeclared here (not in a function)
  163 |         { MODKEY,                       XK_w,           spawn,          {.v = (const char*[]){ BROWSER, NULL } } },
      |                                                                                                ^~~~~~~
make: *** [Makefile:18: dwm.o] Error 1

[LukeSmithxyz]

Manually set in 7c356f7

Might have it read environmental variables later.