Merge pull request #1023 from sjwarner-bp/nth-prime-starter

nth-prime: add starter implementation

exercises/nth-prime/src/main/java/PrimeCalculator.java

+class PrimeCalculator {
+
+    int nth(int nth) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
+}