chore: fix opencensus version in readme (#551)

we are using https://github.com/googleapis/java-shared-dependencies/blob/master/pom.xml#L73

Author: kolea2

README.md

@@ -176,13 +176,13 @@ If you are using Maven, add this to your pom.xml file
 <dependency>
   <groupId>io.opencensus</groupId>
   <artifactId>opencensus-impl</artifactId>
-  <version>0.26.0</version>
+  <version>0.24.0</version>
   <scope>runtime</scope>
 </dependency>
 <dependency>
   <groupId>io.opencensus</groupId>
   <artifactId>opencensus-exporter-trace-stackdriver</artifactId>
-  <version>0.26.0</version>
+  <version>0.24.0</version>
   <exclusions>
     <exclusion>
       <groupId>io.grpc</groupId>
@@ -197,13 +197,13 @@ If you are using Maven, add this to your pom.xml file
 ```
 If you are using Gradle, add this to your dependencies
 ```Groovy
-compile 'io.opencensus:opencensus-impl:0.26.0'
-compile 'io.opencensus:opencensus-exporter-trace-stackdriver:0.26.0'
+compile 'io.opencensus:opencensus-impl:0.24.0'
+compile 'io.opencensus:opencensus-exporter-trace-stackdriver:0.24.0'
 ```
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "io.opencensus" % "opencensus-impl" % "0.26.0"
-libraryDependencies += "io.opencensus" % "opencensus-exporter-trace-stackdriver" % "0.26.0"
+libraryDependencies += "io.opencensus" % "opencensus-impl" % "0.24.0"
+libraryDependencies += "io.opencensus" % "opencensus-exporter-trace-stackdriver" % "0.24.0"
 ```
 
 At the start of your application configure the exporter:
@@ -280,13 +280,13 @@ If you are using Maven, add this to your pom.xml file
 <dependency>
   <groupId>io.opencensus</groupId>
   <artifactId>opencensus-impl</artifactId>
-  <version>0.26.0</version>
+  <version>0.24.0</version>
   <scope>runtime</scope>
 </dependency>
 <dependency>
   <groupId>io.opencensus</groupId>
   <artifactId>opencensus-exporter-stats-stackdriver</artifactId>
-  <version>0.26.0</version>
+  <version>0.24.0</version>
   <exclusions>
     <exclusion>
       <groupId>io.grpc</groupId>
@@ -301,13 +301,13 @@ If you are using Maven, add this to your pom.xml file
 ```
 If you are using Gradle, add this to your dependencies
 ```Groovy
-compile 'io.opencensus:opencensus-impl:0.26.0'
-compile 'io.opencensus:opencensus-exporter-stats-stackdriver:0.26.0'
+compile 'io.opencensus:opencensus-impl:0.24.0'
+compile 'io.opencensus:opencensus-exporter-stats-stackdriver:0.24.0'
 ```
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "io.opencensus" % "opencensus-impl" % "0.26.0"
-libraryDependencies += "io.opencensus" % "opencensus-exporter-stats-stackdriver" % "0.26.0"
+libraryDependencies += "io.opencensus" % "opencensus-impl" % "0.24.0"
+libraryDependencies += "io.opencensus" % "opencensus-exporter-stats-stackdriver" % "0.24.0"
 ```
 
 At the start of your application configure the exporter and enable the Bigtable stats views:
@@ -425,4 +425,4 @@ Java 11 | [![Kokoro CI][kokoro-badge-image-5]][kokoro-badge-link-5]
 [kokoro-badge-image-4]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-bigtable/java8-win.svg
 [kokoro-badge-link-4]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-bigtable/java8-win.html
 [kokoro-badge-image-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-bigtable/java11.svg
-[kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-bigtable/java11.html
+[kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-bigtable/java11.html