Update: add fixer for lines-around-directive (#7217)

Author: not-an-aardvark

docs/rules/lines-around-directive.md

@@ -1,5 +1,7 @@
 # require or disallow newlines around directives (lines-around-directive)
 
+(fixable) The `--fix` option on the [command line](../user-guide/command-line-interface#fix) automatically fixes problems reported by this rule.
+
 Directives are used in JavaScript to indicate to the execution environment that a script would like to opt into a feature such as `"strict mode"`. Directives are grouped together in a [directive prologue](http://www.ecma-international.org/ecma-262/7.0/#directive-prologue) at the top of either a file or function block and are applied to the scope in which they occur.
 
 ```js

lib/rules/lines-around-directive.js

@@ -37,7 +37,8 @@ module.exports = {
                     minProperties: 2
                 }
             ]
-        }]
+        }],
+        fixable: "whitespace"
     },
 
     create(context) {
@@ -88,6 +89,12 @@ module.exports = {
                     expected: expected ? "Expected" : "Unexpected",
                     value: node.expression.value,
                     location
+                },
+                fix(fixer) {
+                    if (expected) {
+                        return location === "before" ? fixer.insertTextBefore(node, "\n") : fixer.insertTextAfter(node, "\n");
+                    }
+                    return fixer.removeRange(location === "before" ? [node.range[0] - 1, node.range[0]] : [node.range[1], node.range[1] + 1]);
                 }
             });
         }