remove uses of deprecated JUnit methods

src/test/java/com/spotify/github/GitHubInstantTest.java

@@ -22,7 +22,7 @@
 
 import static org.hamcrest.core.Is.is;
 import static org.hamcrest.core.IsEqual.equalTo;
-import static org.junit.Assert.assertThat;
+import static org.hamcrest.MatcherAssert.assertThat;
 
 import java.time.Instant;
 import org.junit.Test;

src/test/java/com/spotify/github/http/LinkTest.java

@@ -22,7 +22,7 @@
 
 import static java.util.stream.Collectors.toList;
 import static org.hamcrest.core.Is.is;
-import static org.junit.Assert.assertThat;
+import static org.hamcrest.MatcherAssert.assertThat;
 
 import java.util.Arrays;
 import java.util.List;

src/test/java/com/spotify/github/jackson/GitHubInstantModuleTest.java

@@ -21,7 +21,7 @@
 package com.spotify.github.jackson;
 
 import static org.hamcrest.core.Is.is;
-import static org.junit.Assert.assertThat;
+import static org.hamcrest.MatcherAssert.assertThat;
 
 import com.spotify.github.GitHubInstant;
 import java.io.IOException;

src/test/java/com/spotify/github/v3/clients/GitDataClientTest.java

@@ -102,6 +102,7 @@ public void listMatchingReferences() throws Exception {
   }
 
   @Test
+  @SuppressWarnings("deprecation")
   public void listReferences() throws Exception {
     final CompletableFuture<List<Reference>> fixture =
         completedFuture(json.fromJson(getFixture("tags_list.json"), LIST_REFERENCES));

src/test/java/com/spotify/github/v3/repos/StatusTest.java

@@ -22,8 +22,8 @@
 
 import static com.google.common.io.Resources.getResource;
 import static java.nio.charset.Charset.defaultCharset;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.Is.is;
-import static org.junit.Assert.assertThat;
 
 import com.google.common.io.Resources;
 import com.spotify.github.jackson.Json;

src/test/java/com/spotify/github/v3/repos/requests/RepositoryCreateStatusTest.java

@@ -22,7 +22,7 @@
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.CoreMatchers.is;
-import static org.junit.Assert.assertThat;
+import static org.hamcrest.MatcherAssert.assertThat;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.spotify.github.jackson.Json;