message: Fix internal ftrl doc.
diff: @@ -66,7 +66,7 @@ END
  description: <<END
  That is for rows we have grad for, we update var, accum and linear as follows:
  accum_new = accum + grad * grad
  -linear += grad + (accum_new^(-lr_power) - accum^(-lr_power)) / lr * var
  +linear += grad - (accum_new^(-lr_power) - accum^(-lr_power)) / lr * var
  quadratic = 1.0 / (accum_new^(lr_power) * lr) + 2 * l2
  var = (sign(linear) * l1 - linear) / quadratic if |linear| > l1 else 0.0
  accum = accum_new
  