Update capture_details.sigmf-ext.md (#309)

fix misspelling

extensions/capture_details.sigmf-ext.md

@@ -15,7 +15,7 @@ be used in the `captures` object:
 |name|required|type|unit|description|
 |----|--------|----|----|-----------|
 |`acq_scale_factor`|true|double|N/A|Scale factor of IQ collection from the spectrum analyzer used to convert back to real power.|
-|`attentuation`|true|double|dB|Attenuation applied to the input of the sensor.|
+|`attenuation`|true|double|dB|Attenuation applied to the input of the sensor.|
 |`acquisition_bandwidth`|true|double|Hz|Bandwidth of the recording (if lower than the `samp_rate`.|
 |`start_capture`|true|string|N/A|Time of the first sample of IQ recording. The time is UTC with the format of `yyyy-mm-ddTHH:MM:SSZ`.|
 |`stop_capture`|true|string|N/A|Time of the last sample of IQ recording. The time is UTC with the format of `yyyy-mm-ddTHH:MM:SSZ`.|