Fix NBGL doc typo

[xchapron-ledger]

Description

Rebased version of #78

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (b82507e) 69.09% compared to head (c1d7d92) 69.09%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #407   +/-   ##
=======================================
  Coverage   69.09%   69.09%           
=======================================
  Files          11       11           
  Lines         864      864           
=======================================
  Hits          597      597           
  Misses        267      267           

Flag	Coverage Δ
unittests	69.09% <ø> (ø)

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