add missing import

Author: Lexer11l

slack-api-client/src/test/java/test_with_remote_apis/methods/canvases_Test.java

@@ -26,6 +26,7 @@
 import java.util.List;
 
 import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.notNullValue;
 import static org.hamcrest.CoreMatchers.nullValue;
 import static org.hamcrest.MatcherAssert.assertThat;