Allow number at beginning of :it string

[glts]

I ran into this problem today.

describe 'Increment'
  it '2000 times succeeds'
    let a = Z()
    for i in range(2000)
      let a = a.Increment()
    endfor
    " ...
  end
end

# ...
# Vim(function):E475: Invalid argument: 2000_20times_20succeeds
1..0

I haven't looked into it any further.

[kana]

Thank you for the report. I'll fix it someday.