shellinabox: needs MMU support

Fixes:

  http://autobuild.buildroot.net/results/609ec63d36e235581fe0388c0e1102362743d5b2/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/shellinabox/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_SHELLINABOX
 	bool "shellinabox"
+	depends on BR2_USE_MMU # fork()
 	select BR2_PACKAGE_OPENSSL
 	select BR2_PACKAGE_ZLIB
 	help