351 ean example fix (#537)

* bug/doc: Fix invalid EAN-13 barcode in examples

In the various examples and python-escpos CLI there are a number of uses
of `13243546557687` as an EAN-13 example.  This EAN barcode is invalid
as the checksum should be `0` and not `7`.

```
$ python test_print.py
Traceback (most recent call last):
  File "test_print.py", line 5, in <module>
    p.barcode('13243546557687', 'EAN13', 64, 2, '', '')
  File "/home/pi/fatt-display/lib/python3.7/site-packages/escpos/escpos.py", line 433, in barcode
    bc=bc,
escpos.exceptions.BarcodeCodeError: No Barcode code was supplied (Barcode '13243546557687' not in a valid format for type 'EAN13')
```

This patch set removes `13243546557687` and replaces it with the valid
number `40063813339310`.

In researching the list of [assigned prefixes issued by
G1][g1-prefixes] there seemed to be no "officially" defined test  prefix, so
this change was made to be minimally invasive using the number from the
existing test cases.

Resolves #350

Affects #176

[g1-prefixes]: https://www.gs1.org/standards/id-keys/company-prefix
[test-code]: https://www.barcodelookup.com/4006381333931

---------

Co-authored-by: Brian 'Redbeard' Harrington <redbeard@dead-city.org>

doc/user/usage.rst

@@ -121,7 +121,7 @@ on a USB interface.
     # Print QR Code
     p.qr("You can readme from your smartphone")
     # Print barcode
-    p.barcode('1324354657687','EAN13',64,2,'','')
+    p.barcode('4006381333931','EAN13',64,2,'','')
     # Cut paper
     p.cut()