Use HTTPS links in Zipkin exporter README (#636)

Author: shakuzen

packages/opencensus-exporter-zipkin/README.md

@@ -3,7 +3,7 @@
 
 OpenCensus Zipkin Trace Exporter allows the user to send collected traces with [OpenCensus Node.js](https://github.com/census-instrumentation/opencensus-node) to Zipkin.
 
-[Zipkin](http://zipkin.io/) is a distributed
+[Zipkin](https://zipkin.io/) is a distributed
 tracing system. It helps gather timing data needed to troubleshoot
 latency problems in microservice architectures. It manages both the
 collection and lookup of this data.
@@ -20,7 +20,7 @@ npm install @opencensus/exporter-zipkin
 
 ## Usage
 
-To use [Zipkin](http://zipkin.io/) as your exporter, first, download from any of the three available options on [Quickstart](https://zipkin.io/pages/quickstart.html): through Docker, on Java or manually compiling the source code. Tests were executed running Zipkin with Java, through the following commands on terminal:
+To use [Zipkin](https://zipkin.io/) as your exporter, first, download from any of the three available options on [Quickstart](https://zipkin.io/pages/quickstart.html): through Docker, on Java or manually compiling the source code. Tests were executed running Zipkin with Java, through the following commands on terminal:
 
 ```bash
 wget -O zipkin.jar 'https://search.maven.org/remote_content?g=io.zipkin.java&a=zipkin-server&v=LATEST&c=exec'