MESH-000 Update CONTRIBUTING.md (istio-ecosystem#109)

* Update CONTRIBUTING.md

Update version of istio to be 1.8.6 as it is the min version the `install_istio.sh` file checks for.

* Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -21,9 +21,9 @@ export KUBECONFIG=~/.kube/config
 ```
 * Install [Prerequisites](./docs/Examples.md#Prerequisite) and make sure to install istio control plane in cluster. Alternatively, you can use the script to install istio control plane on the cluster created in previous step:
 
-Mac: `$ADMIRAL_HOME/tests/install_istio.sh 1.7.4 osx` 
+Mac: `$ADMIRAL_HOME/tests/install_istio.sh 1.10.4 osx` 
 
-Linux: `$ADMIRAL_HOME/tests/install_istio.sh 1.7.4 linux`                                                                                            
+Linux: `$ADMIRAL_HOME/tests/install_istio.sh 1.10.4 linux`                                                                                            
 
 * Set up necessary permissions and configurations for Admiral
 
@@ -85,4 +85,4 @@ cd $ADMIRAL_HOME/tests
 ```
 TODO
 ```
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+