stale: removed stale import

Author: rchougule

src/main/java/com/browserstack/client/BrowserStackClient.java

@@ -33,7 +33,6 @@
 import org.apache.http.impl.client.HttpClientBuilder;
 
 import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.Reader;