Fixed some documentation headings to use a space (encode#7364)

Author: adamchainz

docs/api-guide/fields.md

@@ -371,7 +371,7 @@ Corresponds to `django.db.models.fields.TimeField`
 * `format` - A string representing the output format.  If not specified, this defaults to the same value as the `TIME_FORMAT` settings key, which will be `'iso-8601'` unless set. Setting to a format string indicates that `to_representation` return values should be coerced to string output. Format strings are described below. Setting this value to `None` indicates that Python `time` objects should be returned by `to_representation`. In this case the time encoding will be determined by the renderer.
 * `input_formats` - A list of strings representing the input formats which may be used to parse the date.  If not specified, the `TIME_INPUT_FORMATS` setting will be used, which defaults to `['iso-8601']`.
 
-#### `TimeField` format strings
+#### `TimeField` format strings
 
 Format strings may either be [Python strftime formats][strftime] which explicitly specify the format, or the special string `'iso-8601'`, which indicates that [ISO 8601][iso8601] style times should be used. (eg `'12:34:56.000000'`)
 

docs/api-guide/serializers.md

@@ -161,7 +161,7 @@ Each key in the dictionary will be the field name, and the values will be lists
 
 When deserializing a list of items, errors will be returned as a list of dictionaries representing each of the deserialized items.
 
-#### Raising an exception on invalid data
+#### Raising an exception on invalid data
 
 The `.is_valid()` method takes an optional `raise_exception` flag that will cause it to raise a `serializers.ValidationError` exception if there are validation errors.