Inconsistent `Program.range` with other parsers

Flow version: 0.138.0

Expected behavior

When parsing " a ", other parsers like babel/espree(EDIT: espree has {start:0, end:3, range: [1,2]})/acorn returns Program.range equals to [0, 3]

Actual behavior

> require('flow-parser').parse(' a ').range
[ 1, 2 ]

• Link to Try-Flow or Github repo: N/A