internal: Fix the release script to support longer git hash values (#1477)

Author: xerial

scripts/release.rb

@@ -33,8 +33,8 @@
 new_release_notes <<= logs.split(/\n/)
   .reject{|line| line.include?("#{last_version} release notes")}
   .map{|x|
-    rev = x[0..6]
-    "- #{x[8..-1]} [[#{rev}](#{PREFIX}/commit/#{rev})]\n"
+    rev = x[0..8]
+    "- #{x[10..-1]} [[#{rev}](#{PREFIX}/commit/#{rev})]\n"
   }
 
 TMP_RELEASE_NOTES_FILE = "target/release_notes_#{next_version}.md"