deps: update OpenCensus to 0.28.0 for consistency with gRPC (#1242)

Author: elharo

pom.xml

@@ -584,7 +584,7 @@
     <project.xpp3.version>1.1.4c</project.xpp3.version>
     <project.httpclient.version>4.5.13</project.httpclient.version>
     <project.httpcore.version>4.4.14</project.httpcore.version>
-    <project.opencensus.version>0.24.0</project.opencensus.version>
+    <project.opencensus.version>0.28.0</project.opencensus.version>
     <project.root-directory>..</project.root-directory>
     <deploy.autorelease>false</deploy.autorelease>
   </properties>