Use marker for markdown link verification (#708)

* .travis.yml: enable markdown link verification

* doc/proposals,.github: fix incorrect markdown

Author: AlexNPavel

.github/ISSUE_TEMPLATE/feature-request.md

@@ -7,7 +7,7 @@ about: Suggest a feature
 ## Feature Request
 
 **Is your feature request related to a problem? Please describe.**
-A clear and concise description of what the problem is. Example: "I have an issue when [...]"
+A clear and concise description of what the problem is. Example: "I have an issue when (...)"
 
 **Describe the solution you'd like**
 A clear and concise description of what you want to happen. Add any considered drawbacks.

.travis.yml

@@ -2,9 +2,6 @@ language: go
 go_import_path: github.com/operator-framework/operator-sdk
 sudo: required
 
-services:
-- docker
-
 go:
 - 1.10.3
 
@@ -21,10 +18,21 @@ jobs:
       env: CLUSTER=openshift
       script: make test/ci-go
       name: Go on OpenShift
+      services:
+      - docker
     - before_script: hack/ci/setup-openshift.sh
       env: CLUSTER=openshift
       script: make test/ci-ansible
       name: Ansible on OpenShift
+      services:
+      - docker
+    - name: Markdown Link Checker
+      language: bash
+      before_install: true
+      install: true
+      after_success: echo 'Markdown links are correct'
+      after_failure: echo 'Incorrect markdown link detected'
+      script: ./hack/ci/marker
 
 install:
 - curl -Lo dep https://github.com/golang/dep/releases/download/v0.5.0/dep-linux-amd64 && chmod +x dep && sudo mv dep /usr/local/bin/

doc/proposals/leader-for-life.md

@@ -10,7 +10,7 @@ multiple active operators of the same type.
 High availability is not a goal of leader election for operators.
 
 Controller-runtime is adding leader election based on functionality present [in
-client-go](git@github.com:operator-framework/operator-sdk.git). However that
+client-go](https://github.com/kubernetes/client-go/blob/master/tools/leaderelection/leaderelection.go). However that
 implementation allows for the possibility of brief periods during which
 multiple leaders are active.
 

doc/proposals/tls-utilities.md

@@ -62,7 +62,7 @@ We will break down the TLS workflow into the following steps:
 
 	Options:
 
-	* Key usage: [Server, Client or Both] If Server, needs svc obj (cluster.local can be different). If client, needs CN and possible org.
+	* Key usage: (Server, Client or Both) If Server, needs svc obj (cluster.local can be different). If client, needs CN and possible org.
 	* Option to specify signature configuration policy i.e Signing Profile for the certificate.
 
         Outputs: