switch github workflows to 1.18

Author: mattfenwick

.github/workflows/go.yml

@@ -15,7 +15,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.16
+        go-version: 1.18
 
     - name: Build
       run: go build -v ./cmd/cyclonus/main.go

.github/workflows/kind_cni_from_source.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v2
         with:
-          go-version: 1.16
+          go-version: 1.18
 
       - name: Run Cyclonus
         working-directory: hack/kind

docs/developer-guide.md

@@ -2,7 +2,7 @@
 
 ## Setup
 
- - [Get set up with golang 1.16](https://golang.org/dl/)
+ - [Get set up with golang 1.18](https://golang.org/dl/)
  - clone this repo
 
         git clone [email protected]:mattfenwick/cyclonus.git