Fix deprecated assertThat in tests.

src/test/java/org/leumasjaffe/container/EitherFunctionalTest.java

@@ -1,7 +1,7 @@
 package org.leumasjaffe.container;
 
 import static org.hamcrest.CoreMatchers.*;
-import static org.junit.Assert.assertThat;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.Assert.fail;
 
 import org.junit.Before;

src/test/java/org/leumasjaffe/container/EitherStateTest.java

@@ -1,7 +1,7 @@
 package org.leumasjaffe.container;
 
 import static org.hamcrest.CoreMatchers.*;
-import static org.junit.Assert.assertThat;
+import static org.hamcrest.MatcherAssert.assertThat;
 
 import org.junit.Before;
 import org.junit.Test;