Make usage of <code> in headers *not* ugly on small device screens

[toughengineer]

This is similar to
Make usage of <code> in headers not ugly #34
and fixes the issue for small screens.

The base font size is 14px, the size of code and pre elements is supposed to be 11px.
11/14 = 0.7(857142857142), 0.7857 seems to be the good place to truncate it.
So for 14px base size code and pre size will be
14px*0.7857 = 10,9998px which is very close to 11px.

Before the fix:

After the fix:

[koppor]

@toughengineer I stumbled on this PR and saw that there were failing checks, but I could not check. Maybe, you can add a commit to rigger the checks again?

Update: Maybe the errors are because of #60 (comment)?

[toughengineer]

@koppor, here you go.
No idea about the failing checks.

[koppor]

For the record, this is the error:

HTML-Proofer finished successfully.
Inspecting 3 files
..W

Offenses:

script/validate-html:23:40: W: [Correctable] Lint/RedundantStringCoercion: Redundant use of Object#to_s in puts.
  results.errors.each { |err| puts err.to_s }
                                       ^^^^

3 files inspected, 1 offense detected, 1 offense autocorrectable