ruby: use --disable-rubygems

At least for ruby 2.x we need to --disable-rubygems besides removing the
gems files to avoid the requires.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/ruby/ruby.mk

@@ -12,7 +12,7 @@ RUBY_DEPENDENCIES = host-pkgconf host-ruby
 HOST_RUBY_DEPENDENCIES = host-pkgconf
 RUBY_MAKE_ENV = $(TARGET_MAKE_ENV)
 RUBY_MAKE = $(MAKE1)
-RUBY_CONF_OPT = --disable-install-doc --disable-rpath
+RUBY_CONF_OPT = --disable-install-doc --disable-rpath --disable-rubygems
 HOST_RUBY_CONF_OPT = --disable-install-doc \
 	--with-out-ext=curses,openssl,readline \
 	--without-gmp