Fix NOX index baseline value in comment

Fixes #55

Testing CoPilot Workspaces to solve this complicated one line issue ;)

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/adafruit/Adafruit_Sensor/issues/55?shareId=XXXX-XXXX-XXXX-XXXX).

Author: tyeth

Adafruit_Sensor.h

@@ -151,7 +151,7 @@ typedef struct {
     float tvoc;              /**< Total Volatile Organic Compounds, in ppb */
     float voc_index; /**< VOC (Volatile Organic Compound) index where 100 is
                           normal (unitless) */
-    float nox_index; /**< NOx (Nitrogen Oxides) index where 100 is normal
+    float nox_index; /**< NOx (Nitrogen Oxides) index where 1 is normal
                           (unitless) */
     float CO2;       /**< Measured CO2 in parts per million (ppm) */
     float eCO2;      /**< equivalent/estimated CO2 in parts per million (ppm