Remove gopkg finish switch to go11module

[viktorbenei]

Depends on https://github.com/bitrise-io/bitrise-plugins-io/pull/51

[viktorbenei]

bitrise.yml diff without the workflow order change (caused by normalization when you open the yml in the workflow editor):

diff --git a/bitrise.yml b/bitrise.yml
index c533b2c..4de5086 100644
--- a/bitrise.yml
+++ b/bitrise.yml
@@ -5,6 +5,9 @@ app:
   envs:
   - RELEASE_VERSION: 0.0.5
   - BIN_NAME: bitrise-plugins-io
+  - GOFLAGS: -mod=vendor
+    opts:
+      is_expand: false
 workflows:
   create-release:
     title: Create release with Releaseman
@@ -85,9 +88,13 @@ workflows:
         - content: |-
             #!/usr/bin/env bash
             set -ex
-            go get -u -v github.com/golang/dep/cmd/dep
-            dep ensure -v
-            dep ensure -v -update
+
+            rm -rf ./vendor
+            rm -f go.mod go.sum
+
+            go mod init
+            go mod tidy
+            go mod vendor
   go-test:
     steps:
     - script:
@@ -104,7 +111,11 @@ workflows:
         - content: |-
             #!/usr/bin/env bash
             set -ex
+
+            cd /tmp
             go get -u github.com/kisielk/errcheck
+            cd -
+
             errcheck -asserts=true -blank=true $GOLIST_WITHOUT_VENDOR
     - script:
         title: Go lint
@@ -112,7 +123,11 @@ workflows:
         - content: |-
             #!/usr/bin/env bash
             set -ex
+
+            cd /tmp
             go get -u golang.org/x/lint/golint
+            cd -
+
             while read -r line; do
               echo "-> Linting: $line"
               golint_out="$(golint $line)"
@@ -128,6 +143,7 @@ workflows:
         - content: |-
             #!/usr/bin/env bash
             set -ex
+
             go test $(go list ./... | grep -v vendor)
   integration-test:
     steps: