docs: fix regex patterns in samples (#425)

Author: ymc9

docs/the-complete-guide/part1/5-data-validation.md

@@ -82,7 +82,7 @@ We can use data validation to improve our app's robustness in many places. Two s
  ```zmodel
  model Space {
  ...
- slug String @unique @regex('^[0-9a-zA-Z_\-]{4,16}$')
+ slug String @unique @regex('^[0-9a-zA-Z]{4,16}$')
  }
  ```
 

versioned_docs/version-1.x/the-complete-guide/part1/5-data-validation.md

@@ -81,7 +81,7 @@ We can use data validation to improve our app's robustness in many places. Two s
  ```zmodel
  model Space {
  ...
- slug String @unique @regex('^[0-9a-zA-Z_\-]{4,16}$')
+ slug String @unique @regex('^[0-9a-zA-Z]{4,16}$')
  }
  ```