[EDITORIAL] Update billingperiodend.md (#483)

I think we have the wrong word at the very beginning. This is supposed
to be billing period end.

specification/columns/billingperiodend.md

@@ -1,6 +1,6 @@
 # Billing Period End
 
-Billing Period Start represents the [*exclusive*](#glossary:exclusivebound) end date and time of a [*billing period*](#glossary:billing-period). For example, a time period where [BillingPeriodStart](#glossary:billingperiodstart) is '2024-01-01T00:00:00Z' and BillingPeriodEnd is '2024-02-01T00:00:00Z' includes charges for January, since BillingPeriodStart is [*inclusive*](#glossary:inclusivebound), but does not include charges for February since BillingPeriodEnd is *exclusive*.
+Billing Period End represents the [*exclusive*](#glossary:exclusivebound) end date and time of a [*billing period*](#glossary:billing-period). For example, a time period where [BillingPeriodStart](#glossary:billingperiodstart) is '2024-01-01T00:00:00Z' and BillingPeriodEnd is '2024-02-01T00:00:00Z' includes charges for January, since BillingPeriodStart is [*inclusive*](#glossary:inclusivebound), but does not include charges for February since BillingPeriodEnd is *exclusive*.
 
 The BillingPeriodEnd column MUST be present in the billing data. This column MUST be of type [Date/Time Format](#date/timeformat), MUST be an *exclusive* value, and MUST NOT contain null values. The sum of the [BilledCost](#billedcost) column for [*rows*](#glossary:row) in a given *billing period* MUST match the sum of the invoices received for that *billing period* for a [*billing account*](#glossary:billing-account).