Fix continuation in get_field_measurements multi-site example

Same pre-existing bug shape as the one PR 265 already fixed in
get_daily: a list item on a continuation line without the doctest
"... " prefix, which makes doctest end the example mid-bracket
(SyntaxError: '[' was never closed). Found by exec'ing every example
in the four PR-touched functions against the live USGS API.

Reformatted to put each list element on its own properly-prefixed
continuation line, matching the style used elsewhere in this file.
While here, dropped the non-PEP8 spaces around the `=` of keyword
arguments.

After this fix, all 15 doctest examples in the four functions PR 265
touched pass when run with the package imported (15/15 across
get_daily, get_latest_continuous, get_latest_daily,
get_field_measurements; verified live against api.waterdata.usgs.gov).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thodson-usgs

dataretrieval/waterdata/api.py

@@ -1512,10 +1512,12 @@ def get_field_measurements(
         >>> # Get field measurements from multiple sites and
         >>> # parameter codes from the last 20 years
         >>> df, md = dataretrieval.waterdata.get_field_measurements(
-        ...     monitoring_location_id = ["USGS-451605097071701",
-                                          "USGS-263819081585801"],
-        ...     parameter_code = ["62611", "72019"],
-        ...     time = "P20Y"
+        ...     monitoring_location_id=[
+        ...         "USGS-451605097071701",
+        ...         "USGS-263819081585801",
+        ...     ],
+        ...     parameter_code=["62611", "72019"],
+        ...     time="P20Y",
         ... )
     """
     service = "field-measurements"