Shrink the shingle size used for suggestions

The original shingle size (5) is a holdover from long long ago.  We now
know better: Elasticsearch doesn't do anything with shingles larger than
3.  Could go down to 2 to save some space but we prefer having wonderful
suggestions.

This might save some space and this might speed up suggestions.  It won't
take up more space and it won't slow them down.  It is more right then
the old setting.

Change-Id: I480d01abffb5d4fd5fa94ceafabf815e85d720b8