Fixes the issue in which the root html element is added to the cfi

[halmos]

See issue #14 and #10.

Please note: I was not able to understand if the CFI test at:

epub-cfi-resolver/tests/generator.js

Line 64 in 66f0543

cfiStr = 'epubcfi(/2/4/2[!/^[^]^,^;]/2/4[!/foo^^^[^]]/1:10)';

should expected to be

cfiStr = 'epubcfi(/4/2[!/^[^]^,^;]/2/4[!/foo^^^[^]]/1:10)';

or

cfiStr = 'epubcfi(/4/2[!/^[^]^,^;]/4[!/foo^^^[^]]/1:10)';

Currently, the code is producing the first one.