Fix incorrect regex on Person.name field (#1089)

The example regular expression introduced in
10eb9db
does not seem to work as intended, due to nesting a negated range inside
another range:

```
❯ jshell --class-path ~/.m2/repository/com/google/re2j/re2j/1.7/re2j-1.7.jar
|  Welcome to JShell -- Version 17.0.9
|  For an introduction type: /help intro

jshell> com.google.re2j.Pattern p = com.google.re2j.Pattern.compile("^[^[0-9]A-Za-z]+( [^[0-9]A-Za-z]+)*$");
p ==> ^[^[0-9]A-Za-z]+( [^[0-9]A-Za-z]+)*$

jshell> p.matches(pattern, "Protocol Buffers");
$4 ==> false

jshell> p.matches(pattern, "Matt Brown");
$5 ==> false
```

The nesting of ranges in the example is also redundant - if you are
going to specify that only `[A-Za-z]` is valid than including [^0-9]` in
that range is not necessary.

This commit fixes the example regular expression to match the example
"name" mentioned later in the README.

---------

Co-authored-by: Chris Roche <[email protected]>

README.md

@@ -33,7 +33,7 @@ message Person {
   string email = 2 [(validate.rules).string.email = true];
 
   string name = 3 [(validate.rules).string = {
-    pattern:   "^[^[0-9]A-Za-z]+( [^[0-9]A-Za-z]+)*$",
+    pattern:   "^[A-Za-z]+( [A-Za-z]+)*$",
     max_bytes: 256,
   }];
 
@@ -58,7 +58,7 @@ p.Id = 1000
 err = p.Validate() // err: Email must be a valid email address
 p.Email = "[email protected]"
 
-err = p.Validate() // err: Name must match pattern '^[^\d\s]+( [^\d\s]+)*$'
+err = p.Validate() // err: Name must match pattern '^[A-Za-z]+( [A-Za-z]+)*$'
 p.Name = "Protocol Buffer"
 
 err = p.Validate() // err: Home is required

python/README.md

@@ -22,7 +22,7 @@ except ValidationFailed as err:
     print(err)  
     # p.id is not greater than 999
     # p.email is not a valid email
-    # p.name pattern does not match ^[^[0-9]A-Za-z]+( [^[0-9]A-Za-z]+)*$
+    # p.name pattern does not match ^[A-Za-z]+( [A-Za-z]+)*$
     # home is required.
 ```