Removed spaces from top-level directory names.

Spaces tend to cause annoyances in a Unix-style shell environment.
This change fixes that.

54_Letter/java/src/LetterGame.java

@@ -0,0 +1,8 @@
+public class LetterGame {
+
+    public static void main(String[] args) {
+
+        Letter letter = new Letter();
+        letter.play();
+    }
+}