Fix typo

Pointed out by @jbduncan (bazelbuild@1d287fc#commitcomment-22131116).

PiperOrigin-RevId: 156216265

src/main/java/com/google/devtools/build/lib/buildeventstream/transports/BuildEventStreamOptions.java

@@ -43,7 +43,7 @@ public class BuildEventStreamOptions extends OptionsBase {
     name = "experimental_build_event_json_file",
     defaultValue = "",
     optionUsageRestrictions = OptionUsageRestrictions.HIDDEN,
-    help = "If non-empty, write a JOSN serialisation of the build event protocol to that file."
+    help = "If non-empty, write a JSON serialisation of the build event protocol to that file."
   )
   public String buildEventJsonFile;