Minor correction for Java test instructions

This is a minor correction to the instructions for running Java tests.

The instructions as updated in
rapidsai#1004 indicates the following:
```
mvn verify -Dintegration-test=com.nvidia.cuvs.CagraBuildAndSearchIT
```

Per the documentation for the
[`failsafe`](https://maven.apache.org/surefire/maven-failsafe-plugin/examples/single-test.html),
plugin, this commit changes this to the following:
```
mvn verify -Dit.test=com.nvidia.cuvs.CagraBuildAndSearchIT
```

Author: mythrocks

java/README.md

@@ -28,7 +28,7 @@ Run `./build.sh --run-java-tests` from this directory.
 To run a single test:
 ```sh
 cd cuvs-java/
-mvn verify -Dintegration-test=com.nvidia.cuvs.CagraBuildAndSearchIT
+mvn verify -Dit.test=com.nvidia.cuvs.CagraBuildAndSearchIT
 ```
 Be sure to set (manually, if needed) your `LD_LIBRARY_PATH` to include the directory with the appropriate (matching)
 version of `libcuvs.so`.