docs: update example

Signed-off-by: Athan <kgryte@gmail.com>

Author: kgryte

lib/node_modules/@stdlib/_tools/eslint/rules/no-error-string-concat/README.md

@@ -73,14 +73,11 @@ var Linter = require( 'eslint' ).Linter;
 var rule = require( '@stdlib/_tools/eslint/rules/no-error-string-concat' );
 
 var linter = new Linter();
-var result;
-var code;
-
-code = 'throw new Error( \'invalid argument. Value: `\' + value + \'`.\' );';
+var code = 'throw new Error( \'invalid argument. Value: `\' + value + \'`.\' );';
 
 linter.defineRule( 'no-error-string-concat', rule );
 
-result = linter.verify( code, {
+var result = linter.verify( code, {
     'rules': {
         'no-error-string-concat': 'error'
     }