As your columns are Text not date they are sorted alphabetically.
You may do two things,
1. Load your columns as Date
2. Add a new column to your load script which defines the sort order (e.g Oct-14 being 1 and Nov-14 is 2 and so on)
then you can modify the sort order of the chart by changing the sorting attribute of date to Custom and selecting expression and then adding your sort order column to the expression.
You can do an Inline Load
LOAD * INLINE [
Oct 14, 1
Nov 14, 2
Dec 14, 3
Assuming the field name of you date filed is "Date" this should create you a table with months sorted by SortOrder column. You can then use that column in your sort expression of the dimension