message: memory store: don't log warning after each save
  it is annoying, one warning on statup is enough
diff: @@ -971,7 +971,6 @@ function Botkit(configuration) {
  cb(null, botkit.memory_store.teams[team_id]);
  },
  save: function(team, cb) {
  - botkit.log('Warning: using temporary storage. Data will be lost when process restarts.');
  if (team.id) {
  botkit.memory_store.teams[team.id] = team;
  cb(null, team.id);
  @@ -988,7 +987,6 @@ function Botkit(configuration) {
  cb(null, botkit.memory_store.users[user_id]);
  },
  save: function(user, cb) {
  - botkit.log('Warning: using temporary storage. Data will be lost when process restarts.');
  if (user.id) {
  botkit.memory_store.users[user.id] = user;
  cb(null, user.id);
  @@ -1005,7 +1003,6 @@ function Botkit(configuration) {
  cb(null, botkit.memory_store.channels[channel_id]);
  },
  save: function(channel, cb) {
  - botkit.log('Warning: using temporary storage. Data will be lost when process restarts.');
  if (channel.id) {
  botkit.memory_store.channels[channel.id] = channel;
  cb(null, channel.id);
  