Fix more direct links to API docs from README (#132)

Author: chingor13

README.md

@@ -157,14 +157,14 @@ This is not an official Google product.
 [integration-docs]: https://census-instrumentation.github.io/opencensus-php
 [composer]: https://getcomposer.org/
 [pecl]: https://pecl.php.net/
-[never-sampler]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
-[always-sampler]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
-[qps-sampler]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
-[probability-sampler]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
-[echo-exporter]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Exporter/EchoExporter.html
-[file-exporter]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Exporter/FileExporter.html
-[stackdriver-exporter]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Exporter/StackdriverExporter.html
-[logger-exporter]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Exporter/LoggerExporter.html
-[null-exporter]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Exporter/NullExporter.html
-[zipkin-exporter]: http://opencensus.io/opencensus-php/api/OpenCensus/Trace/Exporter/ZipkinExporter.html
+[never-sampler]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
+[always-sampler]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
+[qps-sampler]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
+[probability-sampler]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Sampler/NeverSampleSampler.html
+[echo-exporter]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Exporter/EchoExporter.html
+[file-exporter]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Exporter/FileExporter.html
+[stackdriver-exporter]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Exporter/StackdriverExporter.html
+[logger-exporter]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Exporter/LoggerExporter.html
+[null-exporter]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Exporter/NullExporter.html
+[zipkin-exporter]: https://census-instrumentation.github.io/opencensus-php/api/OpenCensus/Trace/Exporter/ZipkinExporter.html
 [semver]: http://semver.org/