added _.isNumber definition

lodash/lodash-tests.ts

@@ -632,6 +632,8 @@ result = <boolean>_.isNaN(undefined);
 result = <boolean>_.isNull(null);
 result = <boolean>_.isNull(undefined);
 
+result = <boolean>_.isNumber(8.4 * 5);
+
 var mergeNames = {
   'stooges': [
     { 'name': 'moe' },

lodash/lodash.d.ts

@@ -2450,6 +2450,15 @@ declare module _ {
 	**/
 	export function isNull(value: any): boolean;
 
+	/**
+	* Checks if value is a number.
+	*
+	* Note: NaN is considered a number. See http://es5.github.io/#x8.5.
+	* @param value The value to check.
+	* @return True if the value is a number, else false.
+	**/
+	export function isNumber(value: any): boolean;
+
 	/**
 	* Recursively merges own enumerable properties of the source object(s), that don't resolve 
 	* to undefined into the destination object. Subsequent sources will overwrite property 
@@ -2684,13 +2693,6 @@ declare module _ {
 	**/
 	export function isString(object: any): boolean;
 
-	/**
-	* Returns true if object is a Number (including NaN).
-	* @param object Check if this object is a Number.
-	* @return True if `object` is a Number, otherwise false.
-	**/
-	export function isNumber(object: any): boolean;
-
 	/**
 	* Returns true if object is a RegExp.
 	* @param object Check if this object is a RegExp.