internal/worker: fix staticcheck error

Fix these errors:

internal/worker/worker.go:77:10: error strings should not be capitalized (ST1005)
internal/worker/worker.go:77:10: error strings should not end with punctuation or a newline (ST1005)

Change-Id: Id56a96eb0d09799862eec52d829403e6e1d11252
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/370883
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
diff --git a/internal/worker/worker.go b/internal/worker/worker.go
index fdaaf6f..7ef0bf3 100644
--- a/internal/worker/worker.go
+++ b/internal/worker/worker.go
@@ -83,7 +83,7 @@
 		return err
 	}
 	if !b {
-		return errors.New("False positives not inserted.")
+		return errors.New("false positives not inserted")
 	}
 
 	urs, err := st.ListCommitUpdateRecords(ctx, 1)