Re-cut v0.6.0

This patch fixes two problems in commit e5a81bb.

1) There was a problem where the #comment after the IS_RELEASE
variable was casuing the conditional logic to assume this was
a -snapshot release.

2) We collectively agreed that -developer-preview is a bit
of a mouthful for the release taxonomy and this should be
shortened to -preview

This has been confirmed to now drive the proper conditional
generation of a release tag and use the desired "-preview".

Change-Id: I58f2d68862aca34ae0181fe35c2f503e7f5d522a
Signed-off-by: Gregory Haskins <gregory.haskins@gmail.com>

Makefile

@@ -37,8 +37,8 @@
 #   - dist-clean - superset of 'clean' that also removes persistent state
 
 PROJECT_NAME   = hyperledger/fabric
-BASE_VERSION   = 0.6.0-developer-preview
-IS_RELEASE     = true # commit as 'true' only once for a given $(BASE_VERSION)
+BASE_VERSION   = 0.6.0-preview
+IS_RELEASE     = true
 
 ifneq ($(IS_RELEASE),true)
 EXTRA_VERSION ?= snapshot-$(shell git rev-parse --short HEAD)