Fix missing apply_to_spans in OTEP 0152 (open-telemetry#180)

The OTEP text correctly says:
>In addition it is also possible to optionally specify spans and events that the transformation should apply to.

However, the block after that text is missing the apply_to_spans
that the text alludes to. I wrote the text correctly but made a
mistake when copy/pasting the yaml from my experimental codebase.

I consider this to be a non-breaking change. It is a bug fix since
the tag in yaml is supposed to be there according to the text.

oteps/0152-telemetry-schemas.md

@@ -425,7 +425,9 @@ only to events of spans that have the specified name. Here is the structure:
 
 This is similar to the "rename_attributes" transformation supported in "all" and
 "resource" sections. In addition it is also possible to optionally specify spans
-and events that the transformation should apply to. Here is the structure:
+and events that the transformation should apply to (both optional conditions
+must match, if specified, for transformation to be applicable). Here is the
+structure:
 
 ```yaml
     span_events:
@@ -436,6 +438,9 @@ and events that the transformation should apply to. Here is the structure:
               # in the previous version, the values are the new attribute name
               # starting from this version.
 
+            apply_to_spans:
+              # Optional span names to apply to. If empty applies to all spans.
+
             apply_to_events:
               # Optional event names to apply to. If empty applies to all events.
 ```