Restore import path with uppercase characters

I wasn't able to reproduce the issue described in GoogleContainerTools#5492 and GoogleContainerTools#5505, so
this change restores the import path with the uppercase characters
and the `ko://` prefix in the custom build example.

I had to tweak some values to get the integration tests to run,
because I don't have access to the `k8s-skaffold` project. Let's see
if the build passes.

Additional minor changes:

- Bump the ko version in the custom build example.

- Add the full path to the ko binary in the custom build script, in case
  `$GOPATH/bin` is not on the `PATH`.

Once we move to Go 1.16 for our builds, we can use the `go install`
command to install ko in the custom build shell script.

Author: halvards

integration/examples/custom/build.sh

@@ -3,11 +3,12 @@ set -e
 
 if ! [ -x "$(command -v ko)" ]; then
     pushd $(mktemp -d)
-    go mod init tmp; GOFLAGS= go get github.com/google/ko/cmd/ko@v0.6.0
+    curl -L https://github.com/google/ko/archive/v0.8.3.tar.gz | tar --strip-components 1 -zx
+    go build -o $(go env GOPATH)/bin/ko .
     popd
 fi
 
-output=$(ko publish --local --preserve-import-paths --tags= . | tee)
+output=$($(go env GOPATH)/bin/ko publish --local --preserve-import-paths --tags= . | tee)
 ref=$(echo "$output" | tail -n1)
 
 docker tag "$ref" "$IMAGE"

integration/examples/custom/skaffold.yaml

@@ -2,7 +2,7 @@ apiVersion: skaffold/v2beta20
 kind: Config
 build:
   artifacts:
-  - image: github.com/googlecontainertools/skaffold/examples/custom
+  - image: ko://github.com/GoogleContainerTools/skaffold/examples/custom
     custom:
       buildCommand: ./build.sh
       dependencies: