Fix VariableTypes solution errors

- Rename duplicate `decimal` variable
- Remove unnecessary `d` in the `number` double
- Fix type of `dogsOut` and `name` variables
- Suppress unused variable warnings

Author: phrdang

src/com/codefortomorrow/beginner/chapter2/solutions/VariableTypes.java

@@ -8,6 +8,7 @@
  */
 
  public class VariableTypes {
+     @SuppressWarnings("unused")
     public static void main(String[] args) {
         // write your code here
 
@@ -18,16 +19,16 @@ public static void main(String[] args) {
         float decimal = 23.32544f;
 
         // define a double variable on line 21
-        double decimal = 23.2352536d;
+        double number = 23.2352536;
 
         // define a boolean variable on line 24 (Hint: true/false)
-        double dogsOut = true;  // the dogs are out :)
+        boolean dogsOut = true;  // the dogs are out :)
 
         // define a character variable on line 27
         char letter = 'A';
 
         // define a string variable on line 30 
-        char name = "Jeff";
+        String name = "Jeff";
 
     }
  }