Single-letter branch name causes "Lexical error"

[drok]

Describe the bug
Graph fails to render if the branch name is a single letter

To Reproduce
Use a single letter branch name:

 branch A

Expected behavior
A graph should be rendered instead of an error shown.

Screenshots
Broken sample (throws error):

gitGraph
 commit
 branch A
 commit
 checkout A

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Broken sample (branch name given as mainBranchName parameter):

%%{init: { 'gitGraph': {'mainBranchName': 'A'}} }%%
gitGraph
 commit id: " " tag: "v1.0"
 branch branch1 order: 3
 checkout A
 commit id: "1st-commit"

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Working example (graph is rendered):

gitGraph
 commit
 branch Ax
 commit
 checkout Ax

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Code Sample
Broken Sample

Broken Sample with mainBranchName

Working Sample

Desktop (please complete the following information):

• OS: Windows 10
• Browser Chrome Version 105.0.5195.102 (Official Build) (64-bit)
• Version [e.g. 22]