build: fix version dependency

src/Makefile.am

@@ -102,7 +102,7 @@ obj/build.h: FORCE
 	@$(MKDIR_P) $(builddir)/obj
 	@$(top_srcdir)/share/genbuild.sh $(abs_top_builddir)/src/obj/build.h \
 	  $(abs_top_srcdir)
-version.o: obj/build.h
+libbitcoin_common_a-version.$(OBJEXT): obj/build.h
 
 libbitcoin_server_a_CPPFLAGS = $(BITCOIN_INCLUDES)
 libbitcoin_server_a_SOURCES = \