DOC: add missing article to gmm docs
@@ -310,7 +310,7 @@ step we break off a portion of the remaining stick. Each time, we associate the
length of the piece of the stick to the proportion of points that falls into a
group of the mixture. At the end, to represent the infinite mixture, we
associate the last remaining piece of the stick to the proportion of points
-that don't fall into all the other groups. The length of each piece is random
+that don't fall into all the other groups. The length of each piece is a random
variable with probability proportional to the concentration parameter. Smaller
value of the concentration will divide the unit-length into larger pieces of
the stick (defining more concentrated distribution). Larger concentration
