fixup!

Author: benjamingr

doc/api/stream.md

@@ -97,7 +97,7 @@ Watermarks only determine the amount of data a stream buffers before it stops
 asking for more data (via calling `readable._read()`). Watermarks do not
 enforce a strict memory limitation in general. Specific stream 
 implementations may choose to enforce stricter limits but doing so is 
-optional. Specifically, `highWaterMark` a threshold, not a limit.
+optional. Specifically, `highWaterMark` is a threshold, not a limit.
 
 Because [`Duplex`][] and [`Transform`][] streams are both `Readable` and
 `Writable`, each maintains *two* separate internal buffers used for reading and