DOC: incorrect example result for pd.merge_ordered
Exsample result for 'merge_ordered' function  in documentation is wrong.
 [https://pandas-docs.github.io/pandas-docs-travis/generated/pandas.merge_ordered.html?highlight=merge_ordered#pandas.merge_ordered](url)

The result should be:
 
  key  lvalue group  rvalue
0   a          1         a     NaN
1   b          1         a       1.0
2   c          2         a        2.0
3   d         2          a       3.0
4   e         3          a       3.0
5   a         1          b     NaN
6   b         1          b       1.0
7   c          2         b        2.0
8   d          2         b        3.0
9   e          3         b        3.0

 
