add implementation for the incomplete frames test

src/main/java/BowlingGameCalculator.java

@@ -1,5 +1,13 @@
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
 public class BowlingGameCalculator {
     public int score(String playerResult) {
-        return 0;
+        Matcher singleDigit = Pattern.compile("\\d").matcher(playerResult);
+        int playerScore = 0;
+        while (singleDigit.find()) {
+            playerScore += Integer.parseInt(singleDigit.group());
+        }
+        return playerScore;
     }
 }