fix: typos in documentation files (#3186)

* Update CannotSubtractException.java

* Update CachingTest.java

* Update App.java

* Update caching.urm.puml

* Update update-method.urm.puml

money/src/main/java/com/iluwatar/CannotSubtractException.java

@@ -1,6 +1,6 @@
 package com.iluwatar;
 /**
- * An exception for when the user tries to subtract two diffrent currencies or subtract an amount he doesn't have.
+ * An exception for when the user tries to subtract two different currencies or subtract an amount he doesn't have.
  */
 public class CannotSubtractException extends Exception {
   /**
@@ -12,4 +12,4 @@ public class CannotSubtractException extends Exception {
     super(message);
   }
 
-}
+}