mkmf.rb: fix typo

* lib/mkmf.rb (configuration): fix typo, should never return nil.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36444 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/mkmf.rb

@@ -1797,7 +1797,7 @@ INCFLAGS = -I. #$INCFLAGS
 DEFS     = #{CONFIG['DEFS']}
 CPPFLAGS = #{extconf_h}#{$CPPFLAGS}
 CXXFLAGS = $(CFLAGS) #{CONFIG['CXXFLAGS']}
-ldflags  = #{$LDFLAGS.tr!("\0", " ")}
+ldflags  = #{$LDFLAGS.tr("\0", " ")}
 dldflags = #{$DLDFLAGS} #{CONFIG['EXTDLDFLAGS']}
 ARCH_FLAG = #{$ARCH_FLAG}
 DLDFLAGS = $(ldflags) $(dldflags) $(ARCH_FLAG)