gluon.mk: fix indentation

A leading tab character usually marks recipe lines in Makefiles;
non-recipe lines must be indented using spaces.

The incorrect tab character doesn't seen to have caused any issues in
this case, but it should be fixed nonetheless, if only for consistency.

package/gluon.mk

@@ -4,7 +4,7 @@ PKG_FILE_DEPENDS += $(GLUON_MK)
 PKG_BUILD_DEPENDS += luasrcdiet/host
 
 ifneq ($(wildcard ./luasrc/.),)
-	PKG_CONFIG_DEPENDS += CONFIG_GLUON_MINIFY
+  PKG_CONFIG_DEPENDS += CONFIG_GLUON_MINIFY
 endif
 
 ifneq ($(wildcard ./src/respondd.c),)