typo

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1908481 13f79535-47bb-0310-9956-ffa450edef68

poi/src/main/java/org/apache/poi/ss/format/CellElapsedFormatter.java

@@ -181,7 +181,7 @@ public class CellElapsedFormatter extends CellFormatter {
             return Math.pow(10, len);
         default:
             throw new IllegalArgumentException(
-                    "Uknown elapsed time spec: " + type);
+                    "Unknown elapsed time spec: " + type);
         }
     }