common.mk: prefix timestamp file by "."

* common.mk (ENC_TRANS_D): prefix by "." to clarify that timestamp
  file for build directory is under the build directory.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49713 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

common.mk

@@ -29,7 +29,7 @@ EXTCONF       = extconf.rb
 LIBRUBY_EXTS  = ./.libruby-with-ext.time
 REVISION_H    = ./.revision.time
 PLATFORM_D    = ./$(PLATFORM_DIR)/.time
-ENC_TRANS_D   = enc/trans/.time
+ENC_TRANS_D   = ./enc/trans/.time
 RDOCOUT       = $(EXTOUT)/rdoc
 HTMLOUT       = $(EXTOUT)/html
 CAPIOUT       = doc/capi