Issue 199: Replaced assertj assetions in nth-prime test with junit and hamcrest assertions. Removed assertj from nth-prime gradle build file. (#215)

exercises/nth-prime/build.gradle

 
 dependencies {
   testCompile "junit:junit:4.12"
-  testCompile "org.assertj:assertj-core:3.2.0"
 }
 test {
   testLogging {

exercises/nth-prime/src/test/java/PrimeTest.java

 import org.junit.Test;
 import org.junit.Ignore;
 
-import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
 
 public class PrimeTest {
 
     @Test
     public void testFirstPrime() {
-        assertThat(Prime.nth(1)).isEqualTo(2);
+        assertThat(Prime.nth(1), is(2));
     }
 
     @Ignore
     @Test
     public void testSecondPrime() {
-        assertThat(Prime.nth(2)).isEqualTo(3);
+        assertThat(Prime.nth(2), is(3));
     }
 
     @Ignore
     @Test
     public void testSixthPrime() {
-        assertThat(Prime.nth(6)).isEqualTo(13);
+        assertThat(Prime.nth(6), is(13));
     }
 
     @Ignore
     @Test
     public void testBigPrime() {
-        assertThat(Prime.nth(10001)).isEqualTo(104743);
+        assertThat(Prime.nth(10001), is(104743));
     }
 
     @Ignore