Switch to SHA-256 for RPM  package signatures

SHA-1 is not supported anymore by recent RPM-based distributions
and therefore packages need to be signed with SHA-256.

Change-Id: I4fca85852b4221e3dc5c45b6142a99c097f6e321
diff --git a/yum-repo/Makefile b/yum-repo/Makefile
index a598511..d39d99d 100644
--- a/yum-repo/Makefile
+++ b/yum-repo/Makefile
@@ -55,7 +55,7 @@
 	echo "%_signature gpg" > ~/.rpmmacros
 	echo "%_gpg_name  $(PGP_USER)" >> ~/.rpmmacros
 	echo '%__gpg_sign_cmd %{__gpg} \
- gpg --force-v3-sigs --digest-algo=sha1 --batch --no-verbose --no-armor \
+ gpg --force-v3-sigs --digest-algo=sha256 --batch --no-verbose --no-armor \
  --passphrase-fd 3 --no-secmem-warning -u "%{_gpg_name}" \
  -sbo %{__signature_filename} %{__plaintext_filename}' >>  ~/.rpmmacros
 	rpm --addsign server/*rpm