Rna-transcription: change to object based implementation

See issue #177

exercises/rna-transcription/src/example/java/RnaTranscription.java

 public class RnaTranscription {
 
-    public static String ofDna(String strand) {
+    public String ofDna(String strand) {
         StringBuilder sb = new StringBuilder();
         for (char c : strand.toCharArray()) {
             switch (c) {

exercises/rna-transcription/src/test/java/RnaTranscriptionTest.java

 import org.junit.Assert;
-import org.junit.Test;
+import org.junit.Before;
 import org.junit.Ignore;
+import org.junit.Test;
 
 public class RnaTranscriptionTest {
 
+    private RnaTranscription rnaTranscription;
+
+    @Before
+    public void setUp() {
+        rnaTranscription = new RnaTranscription();
+    }
 
     @Test
     public void testRnaTranscriptionOfEmptyDnaIsEmptyRna() {
-        Assert.assertEquals("", RnaTranscription.ofDna(""));
+        Assert.assertEquals("", rnaTranscription.ofDna(""));
     }
 
     @Ignore
     @Test
     public void testRnaTranscriptionOfCytosineIsGuanine() {
-        Assert.assertEquals("G", RnaTranscription.ofDna("C"));
+        Assert.assertEquals("G", rnaTranscription.ofDna("C"));
     }
 
     @Ignore
     @Test
     public void testRnaTranscriptionOfGuanineIsCytosine() {
-        Assert.assertEquals("C", RnaTranscription.ofDna("G"));
+        Assert.assertEquals("C", rnaTranscription.ofDna("G"));
     }
 
     @Ignore
     @Test
     public void testRnaTranscriptionOfThymineIsAdenine() {
-        Assert.assertEquals("A", RnaTranscription.ofDna("T"));
+        Assert.assertEquals("A", rnaTranscription.ofDna("T"));
     }
 
     @Ignore
     @Test
     public void testRnaTranscriptionOfAdenineIsUracil() {
-        Assert.assertEquals("U", RnaTranscription.ofDna("A"));
+        Assert.assertEquals("U", rnaTranscription.ofDna("A"));
     }
 
     @Ignore
     @Test
     public void testRnaTranscription() {
-        Assert.assertEquals("UGCACCAGAAUU", RnaTranscription.ofDna("ACGTGGTCTTAA"));
+        Assert.assertEquals("UGCACCAGAAUU", rnaTranscription.ofDna("ACGTGGTCTTAA"));
     }
 }