Update Tutorial with links to 1.77 api docs

[chebizarro]

This pull request updates the Tutorial lex files with the link to the correct version of the API docs as generated by Sphinx.

• [X ] I hereby agree to dual licence this and any previous contributions under both
  the Biopython License Agreement AND the BSD 3-Clause License.

• [X ] I have read the CONTRIBUTING.rst file, have run flake8 locally, and
  understand that AppVeyor and TravisCI will be used to confirm the Biopython unit
  tests and style checks pass with these changes.

• [ X] I have added my name to the alphabetical contributors listings in the files
  NEWS.rst and CONTRIB.rst as part of this pull request, am listed
  already, or do not wish to be listed. (This acknowledgement is optional.)

[codecov]

Codecov Report

Merging #2903 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2903   +/-   ##
=======================================
  Coverage   83.96%   83.96%           
=======================================
  Files         321      321           
  Lines       52126    52126           
=======================================
  Hits        43770    43770           
  Misses       8356     8356           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update adac231...5372488. Read the comment docs.

[peterjc]

See also #2904 and #2905 for updating how we link to the API docs in future.