Duplicate message definition error when generating .po file.

[cryptonerdcn]

In some environments, trying to run the generating language .po file command will cause an error like this:

po/messages.pot:964: duplicate message definition...
po/messages.pot:3: ...this is the location of the first definition

It looks like:

#: src/ch01-00-getting-started.md:13
#: src/ch01-00-getting-started.md:127
#: src/ch02-07-starknet-js.md:11
#: src/ch03-00-architecture.md:26
#: src/ch03-02-sequencers.md:52
#: src/ch03-02-sequencers.md:211
#: src/ch03-04-nodes.md:66
#: src/ch03-04-nodes.md:350
#: src/ch03-04-nodes.md:420
#: src/ch03-05-layer-3.md:18
msgid ""
msgstr ""

It was because of this. google/mdbook-i18n-helpers#64

[cryptonerdcn]

Will be fixed by #214

[omarespejel]

Fixed by @cryptonerdcn, thanks!