Fixes #179: Migration of current travis ci to github-actions ci. (#244)

##### ISSUE TYPE
<!--- Pick one below and delete the rest: -->
 - Feature Pull Request

Fix for issue [githib-actions](#179)

##### SUMMARY

-  Updated the golint path to $GOPATH/bin/golint to fix github-actions build failure.
-  Added docker push action step in current CI steps.
-  Added helm release step along with missing "helm init".

Checklist for Enabling github actions:
make sure to add below secrets in repo/settings/secrets
- GH_TOKEN(github access token of **charts** repo)
- DOCKER_USERNAME and DOCKER_PASSWORD (for **infracloud/botkube** repo).
- That's it, by merging this PR, first github-actions workflow for botkube should be triggered :) 

For reference the tested CI workflows on my repos:

- [with helm release](https://github.com/ameydev/botkube/runs/434885674?check_suite_focus=true)
- [Normal workflow with docker push and helm release skipped](https://github.com/ameydev/botkube/runs/434903893?check_suite_focus=true)

.github/workflows/ci.yml

@@ -0,0 +1,62 @@
+name: CI
+on:
+  push:
+  pull_request:
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    env:
+      GO111MODULE: on
+      GOPATH: /home/runner/work/botkube
+      GOBIN: /home/runner/work/botkube/bin
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: Setup Go
+      uses: actions/setup-go@v1
+      with:
+        go-version: 1.13
+    - name: install golint
+      run: |
+        go get -u golang.org/x/lint/golint
+    - name: Before build
+      run: |
+        echo Workflow trigger - ${{ github.event_name }}
+        ./hack/verify-gofmt.sh
+        ./hack/verify-govet.sh
+        ./hack/verify-golint.sh
+        go mod verify
+    - name: make test, make build, make docker-image
+      run: |
+        make test
+        make
+        make container-image
+    - name: Push docker images
+      if: success() &&  github.event_name  == 'push'  && endsWith(github.ref ,'develop')
+      run: |
+        docker login -u ${{ secrets.DOCKER_USERNAME }} -p ${{ secrets.DOCKER_PASSWORD }}
+        docker push infracloudio/botkube:latest
+    - name: Install helm
+      if: success() &&  github.event_name  == 'push'  && endsWith(github.ref ,'develop')
+      run: |
+        curl https://raw.githubusercontent.com/kubernetes/helm/master/scripts/get > get_helm.sh
+        chmod +x get_helm.sh
+        ./get_helm.sh
+        helm lint helm/botkube
+    - name: Release Helm template
+      if: success() &&  github.event_name  == 'push'  && endsWith(github.ref ,'develop')
+      run: |
+        cd ..
+        git config --global user.email "botkube-ci@infracloud.io"
+        git config --global user.name "BotKube CI"
+        git clone https://github.com/infracloudio/charts.git
+        cd charts
+        git fetch
+        git branch
+        git pull origin gh-pages
+        helm init --client-only
+        helm package --app-version v9.99.9-dev --version v9.99.9-dev ${{ github.workspace }}/helm/botkube/
+        helm repo index --url https://infracloudio.github.io/charts --merge index.yaml .
+        git add .
+        git commit -m "Update BotKube latest helm chart"
+        git push https://${{ secrets.GH_TOKEN }}@github.com/infracloudio/charts.git

hack/verify-golint.sh

@@ -31,7 +31,7 @@ find_files() {
     \) -name '*.go'
 }
 
-bad_files=$(find_files | xargs -I@ bash -c "golint @")
+bad_files=$(find_files | xargs -I@ bash -c "$GOPATH/bin/golint @")
 if [[ -n "${bad_files}" ]]; then
   echo "${bad_files}"
   exit 1