Update binary_sensor.iss.markdown (home-assistant#4077)

Brent Saltzman · fabaff · commit 43f72c00e84e · 2017-11-27T07:54:41.000+01:00
Fixed typo.
diff --git a/source/_components/binary_sensor.iss.markdown b/source/_components/binary_sensor.iss.markdown
@@ -28,7 +28,7 @@ binary_sensor:
 {% configuration %}
 show_on_map:
   description: Option to show the position of the ISS on the map.
-  required: optionsl
+  required: optional
   default: false
   type: string
 {% endconfiguration %}
