Update supported Golang version to Go 1.18

.github/workflows/go.yaml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        go: ['1.15', '1.16', '1.17']
+        go: ['1.16', '1.17', '1.18']
       fail-fast: false
     env:
       OS: ${{ matrix.os }}
@@ -29,7 +29,7 @@ jobs:
 
       - name: Get Build Tools
         run: |
-          GO111MODULE=on go get github.com/ory/go-acc
+          GO111MODULE=on go install github.com/ory/go-acc
 
       - name: Add $GOPATH/bin to $PATH
         run: |
@@ -64,7 +64,7 @@ jobs:
 
     strategy:
       matrix:
-        go: ['1.15', '1.16', '1.17']
+        go: ['1.16', '1.17', '1.18']
       fail-fast: false
     env:
       OS: windows-latest