added task for updating chromosome names (closes #348)

lib/tasks/update_mt_chromosome_name.rake

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+namespace :snps do
+  desc "change mitochondrial snp names from 'mt' to 'm'."
+  task :update_mt_snps => :environment do
+    Snp.where(:chromosome => "MT").each do |s|
+      s.chromosome = "M"
+      s.position = s.position.strip
+      s.save
+    end
+  end
+end