build: rearrange go path order on windows

If PATH comes first, an older version of Go is used that cannot install
dependencies that use features of newer versions of Go, which we just
installed.

.circleci/config.yml

@@ -179,7 +179,7 @@ jobs:
       - run:
           name: Install golang dependencies
           command: |
-            export PATH=$PATH:/c/go/bin:/c/gopath/bin
+            export PATH=/c/go/bin:/c/gopath/bin:$PATH
             make deps
       - run:
           name: Pre-download docker test image
@@ -187,13 +187,13 @@ jobs:
       - run:
           name: Build nomad
           command: |
-            export PATH=$PATH:/c/go/bin:/c/gopath/bin
+            export PATH=/c/go/bin:/c/gopath/bin:$PATH
             go build -o $GOBIN\nomad.exe
       - run:
           name: Run tests with gotestsum
           command: |
             # Only test docker driver tests for now
-            export PATH=$PATH:/c/go/bin:/c/gopath/bin
+            export PATH=/c/go/bin:/c/gopath/bin:$PATH
             gotestsum --format=short-verbose \
               --junitfile $GOTESTSUM_PATH/results.xml \
               github.com/hashicorp/nomad/drivers/docker \