TZDATA_VER in javazip/Makefile

[Xueming Shen]

Okutsu-san

It appears the variable

TZDATA_VER = `$(GREP) '^tzdata' $(TZDATA)VERSION`

in javazip/Makefile does not get evaluated correctly in bash here.

I replaced it with

TZDATA_VER := $(subst tzdata,,$(shell $(GREP) '^tzdata' $(TZDATA)VERSION))

to get the correct version string and also remove the
the prefix "tzdata". I don't see the javazic really uses
this version info, so guess the removal of "tzdata" should
be OK. Let me know if I'm wrong.

Here is the webrev for this change.

http://cr.openjdk.java.net/~sherman/jdk8_threeten/javazic/webrev/

-Sherman