[BUGFIX] Fixed max length check for strings in create/wizard

[GLobyNew]

My first real pull request for this project.

tldr: if you create a custom .yaml with max attribute for string, for example:

---
priority: 1
name: "Bank Card"
prefix: "cards"
name_from:
  - "bankname"
welcome: "🧪 Creating Bank Card entry"
attributes:
  - name: "bankname"
    type: "string"
    prompt: "Bank Name"
    min: 1
    max: 255

It will fail check for max length all the time:

🌟 Welcome to the secret creation wizard (gopass create)!
🧪 Hint: Use 'gopass edit -c' for more control!
[ 0] Website login
[ 1] Bank Card

Please select the type of secret you would like to create (q to abort) [0]: 1
1
🧪 Creating Bank Card entry
  [1] Bank Name                              []: Test
❌ bankname is too long (at most 255)

Turns out wizard was checking v.Min value instead of v.Max
Now works as expected.
All internal tests were passed.

[dominikschulz]

Oh, that's a nice find. Thank you!