cmd/worker/Dockerfile: switch to 1.18

Use Go 1.18 to build and run the vuln worker.

Change-Id: I1dc24ce515feb8e22c5488ef4ae0f714a4495011
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/393838
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

cmd/worker/Dockerfile

@@ -5,7 +5,7 @@
 # This Dockerfile expects the build context to be the repo root.
 
 ################################################################
-FROM golang:1.17.3 AS builder
+FROM golang:1.18.0 AS builder
 # If you change the Go version above, change the FROM line below as well.
 
 # Set the working directory outside $GOPATH to ensure module mode is enabled.
@@ -28,7 +28,7 @@ COPY . /src
 RUN go build -mod=readonly ./cmd/worker
 
 ################################################################
-FROM golang:1.17.3
+FROM golang:1.18.0
 
 LABEL maintainer="Go VulnDB Team <go-vulndb-team@google.com>"