Fixed typo in crossbeam-complex.md (#610)

Author: p0lunin

src/concurrency/thread/crossbeam-complex.md

@@ -3,7 +3,7 @@
 [![crossbeam-badge]][crossbeam] [![cat-concurrency-badge]][cat-concurrency]
 
 This example uses the [crossbeam] and [crossbeam-channel] crates to create
-a parallel pipline, similar to that described in the ZeroMQ [guide]
+a parallel pipeline, similar to that described in the ZeroMQ [guide]
 There is a data source and a data sink, with data being processed by two worker
 threads in parallel on its way from the source to the sink.