Fix MW capacity column name to match AEMO xlsx header

Change _COL_CAPACITY_MW from 'Unit Capacity (MW AC)' to
'Agg Nameplate Capacity (MW AC)' (column S, row 4) to correctly
read the aggregated nameplate MW capacity from the AEMO Generation
Information spreadsheet.

app/services/gen_info_fetcher.py

@@ -44,7 +44,7 @@ _COL_NAME       = "Unit Name"
 _COL_TECH       = "Technology Type"
 _COL_STATUS       = "Commitment Status"
 _COL_REGION       = "Region"
-_COL_CAPACITY_MW  = "Unit Capacity (MW AC)"
+_COL_CAPACITY_MW  = "Agg Nameplate Capacity (MW AC)"
 _COL_CAPACITY_MWH = "Agg Nameplate Storage Capacity (MWh)"
 
 CACHE_TTL = timedelta(hours=24)