doc: update go1.8 release notes after TxOptions change

Missed the release notes when updating the sql API.

Fixes #18825

Change-Id: I89056d46939ad4fc99590f3434d2881f5764e1b6
Reviewed-on: https://go-review.googlesource.com/35915Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.8.html

@@ -859,11 +859,12 @@ crypto/x509: return error for missing SerialNumber (CL 27238)
     <p>
       The <a href="/pkg/database/sql#IsolationLevel"><code>IsolationLevel</code></a>
       can now be set when starting a transaction by setting the isolation level
-      on the <code>Context</code> then passing that <code>Context</code> to
-      <a href="/pkg/database/sql#DB.BeginContext"><code>DB.BeginContext</code></a>.
+      on <a href="/pkg/database/sql#TxOptions.Isolation"><code>TxOptions.Isolation</code></a> and passing
+      it to <a href="/pkg/database/sql#DB.BeginTx"><code>DB.BeginTx</code></a>.
       An error will be returned if an isolation level is selected that the driver
       does not support. A read-only attribute may also be set on the transaction
-      with <a href="/pkg/database/sql/#ReadOnlyContext"><code>ReadOnlyContext</code></a>.
+      by setting <a href="/pkg/database/sql/#TxOptions.ReadOnly"><code>TxOptions.ReadOnly</code></a>
+      to true.
     </p>
     <p>
       Queries now expose the SQL column type information for drivers that support it.