Fix typo.

Author: Marcelo Vanzin

launcher/src/test/java/org/apache/spark/launcher/LauncherServerSuite.java

@@ -177,7 +177,7 @@ public void testStreamFiltering() throws Exception {
         client.send(new EvilPayload());
       } catch (SocketException se) {
         // SPARK-21522: this can happen if the server closes the socket before the full message has
-        // been written, so it's expected. It may cause false positives through (socket errors
+        // been written, so it's expected. It may cause false positives though (socket errors
         // happening for other reasons).
       }