Fix missing comma in get_reference_table doctest example

[thodson-usgs]

The second example block in get_reference_table's docstring is unrunnable — collection="parameter-codes" and query={...} are on separate lines with no comma between them, so the doctest text would not parse as a valid Python call.

Before (broken)

```python

ref, md = dataretrieval.waterdata.get_reference_table(
... collection="parameter-codes"
... query={'id': '00001,00002'}
... )
```

After

```python

ref, md = dataretrieval.waterdata.get_reference_table(
... collection="parameter-codes",
... query={"id": "00001,00002"},
... )
```

(Single quotes inside the dict are normalized to double quotes to match the rest of the file's style — drive-by, no functional change.)

Why

Surfaced while running each public-function docstring example against the live USGS OGC API as part of PR #229's verification pass.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes a syntax error in the get_reference_table docstring example so the illustrated multi-line function call is valid Python, improving documentation reliability for the waterdata API.

Changes:

• Add the missing comma between collection=... and query=... in the second example block.
• Normalize the example dict quoting to double quotes for consistency within the docstring.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.