Add `_` to some term constants for consistency.

I am working to auto generate classes for grandquista/Lua-ReQL@3a44f052f2e41403abacbabbb5ccff4723e364a9 from a list of constant names.

These terms do not fit the rules that I am using because they are missing an `_` between words.

Terms changed:
`CONCATMAP`
`ORDERBY`
`TYPEOF`
`FUNCALL`
`FOREACH`
`GEOJSON`
`TO_GEOJSON`