Use raw string for regex to avoid SyntaxWarning

This fixes the following warnings:

```python
/home/patrick/virtualenvs/conda/envs/hexrdgui/src/hexrdgui/hexrdgui/llnl_import_tool_dialog.py:739: SyntaxWarning: "\d" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\d"? A raw string is also an option.
  image = re.sub("CAMERA-\d{2}-", "CAMERA-*-", selected_file)
/home/patrick/virtualenvs/conda/envs/hexrdgui/src/hexrdgui/hexrdgui/llnl_import_tool_dialog.py:740: SyntaxWarning: "\d" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\d"? A raw string is also an option.
  files = re.sub("-\d{3}.h", "-*.h", image)
```

Signed-off-by: Patrick Avery <patrick.avery@kitware.com>

Author: psavery

hexrdgui/llnl_import_tool_dialog.py

@@ -736,8 +736,8 @@ def load_detector_images(self):
         # TD_TC000-000_FIDDLE_CAMERA-02-DB_SHOT_RAW-FIDDLE-CAMERA_N240717-001-999.h5
         # ->
         # TD_TC000-000_FIDDLE_CAMERA-*-DB_SHOT_RAW-FIDDLE-CAMERA_N240717-001-*.h5
-        image = re.sub("CAMERA-\d{2}-", "CAMERA-*-", selected_file)
-        files = re.sub("-\d{3}.h", "-*.h", image)
+        image = re.sub(r"CAMERA-\d{2}-", "CAMERA-*-", selected_file)
+        files = re.sub(r"-\d{3}.h", "-*.h", image)
 
         # Sort matched files. We know that those ending in -999 are data files.
         # Dark files may have different values at the end (-003, -005, etc.) so