Add bump since git ref

ci/bump-since.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+if [ ! -z $1 ]; then
+    SINCE="since:$1"
+fi
+bundle exec fastlane bump $SINCE

fastlane/Fastfile

@@ -23,7 +23,13 @@ logname = "CHANGELOG.txt"
 desc "Bump version"
 lane :bump do |options|
     unless options[:only]
+        if options[:since]
+            between = [options[:since], "HEAD"]
+        else
+            between = nil
+        end
         log = changelog_from_git_commits(
+            between: between,
             pretty: "* %s",
             date_format: "short"
         )