docs: fix markdown lint

Author: vkarpov15

docs/migrating_to_6.md

@@ -153,6 +153,7 @@ However, this behavior was a source of confusion in some cases, so in Mongoose 7
 ```javascript
 mongoose.set('strictQuery', false);
 ```
+
 In a test suite, it may be useful to set `strictQuery` to `throw`, which will throw exceptions any time a query references schema that doesn't exist, which could help identify a bug in your tests or code.
 
 Here's an example of the effect of `strictQuery`:
@@ -520,7 +521,7 @@ The `reconnectTries` and `reconnectInterval` options have been removed since the
 The MongoDB node driver will always attempt to retry any operation for up to `serverSelectionTimeoutMS`, even if MongoDB is down for a long period of time.
 So, it will never run out of retries or try to reconnect to MongoDB.
 
-## Lodash `.isEmpty()` returns true for ObjectIds #{lodash-object-id}
+## Lodash `.isEmpty()` returns true for ObjectIds {#lodash-object-id}
 
 Lodash's `isEmpty()` function returns true for primitives and primitive wrappers.
 `ObjectId()` is an object wrapper that is treated as a primitive by Mongoose.
@@ -534,7 +535,7 @@ if (!(val instanceof Types.ObjectId) && _.isEmpty(val)) {
 }
 ```
 
-## Removed `mongoose.modelSchemas` #{model-schemas}
+## Removed `mongoose.modelSchemas` {#model-schemas}
 
 The `mongoose.modelSchemas` property was removed. This may have been used to delete a model schema.
 
@@ -546,7 +547,6 @@ delete mongoose.modelSchemas.User;
 delete mongoose.deleteModel('User');
 ```
 
-
 ## TypeScript changes
 
 The `Schema` class now takes 3 generic params instead of 4. The 3rd generic param, `SchemaDefinitionType`, is now the same as the 1st generic param `DocType`. Replace `new Schema<UserDocument, UserModel, User>(schemaDefinition)` with `new Schema<UserDocument, UserModel>(schemaDefinition)`

docs/migrating_to_7.md

@@ -339,7 +339,7 @@ If you want to use Bluebird for all promises globally, you can do the following:
 global.Promise = require('bluebird');
 ```
 
-## Deprecated `keepAlive` #{deprecated-keepalive}
+## Deprecated `keepAlive` {#deprecated-keepalive}
 
 Before Mongoose 5.2.0, you needed to enable the `keepAlive` option to initiate [TCP keepalive](https://tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html) to prevent `"connection closed"` errors.
 However, `keepAlive` has been `true` by default since Mongoose 5.2.0, and the `keepAlive` is deprecated as of Mongoose 7.2.0.