go-swagger: fix panic

This is an attempt to fix go-swagger panic under Golang 1.13.

Details:
 * https://github.com/go-openapi/jsonpointer/pull/4
 * https://github.com/go-swagger/go-swagger/pull/2059

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit 93f9b902af89f82367d750aa871d40f25ccd99ca)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile

@@ -80,10 +80,12 @@ RUN set -x \
 
 FROM base AS swagger
 # Install go-swagger for validating swagger.yaml
-ENV GO_SWAGGER_COMMIT c28258affb0b6251755d92489ef685af8d4ff3eb
+# This is https://github.com/kolyshkin/go-swagger/tree/golang-1.13-fix
+# TODO: move to under moby/ or fix upstream go-swagger to work for us.
+ENV GO_SWAGGER_COMMIT 5793aa66d4b4112c2602c716516e24710e4adbb5
 RUN set -x \
 	&& export GOPATH="$(mktemp -d)" \
-	&& git clone https://github.com/go-swagger/go-swagger.git "$GOPATH/src/github.com/go-swagger/go-swagger" \
+	&& git clone https://github.com/kolyshkin/go-swagger.git "$GOPATH/src/github.com/go-swagger/go-swagger" \
 	&& (cd "$GOPATH/src/github.com/go-swagger/go-swagger" && git checkout -q "$GO_SWAGGER_COMMIT") \
 	&& go build -o /build/swagger github.com/go-swagger/go-swagger/cmd/swagger \
 	&& rm -rf "$GOPATH"