docs: correct typo in comment (#568)
docs: correct typo in comment (#568)

Using a sessionId as number, it causes the following error in
`peg$parsetemplate`:
input.charCodeAt is not a function

Fixes #277

Co-authored-by: Giuseppe Verni <3f90eed29768498da8638ceed29da433915e9b10@gmail.com>
googleapis/nodejs-dialogflow,googleapis/nodejs-dialogflow