Fix spearmint-lite.py indexing bug

Chooser.next() returns candidates[best], which is an integer index from the
candidates list that next() receives as an argument.  spearmint-lite.py
constructs populates that argument with indexes into the `grid` variable
rather than its own local `candidates` variable which is a subset of the rows
of `grid`.
Merge pull request #6 from jaberg/indexing_bug_maybe

Fix spearmint-lite.py indexing bug?