Merge pull request #4020 from watteja/patch-7

Part13c - fix broken links

Author: vejol

src/content/13/en/part13c.md

@@ -640,7 +640,7 @@ module.exports = Membership
 
 So we have given the connection table a name that describes it well, <i>membership</i>. There is not always a relevant name for a connection table, in which case the name of the connection table can be a combination of the names of the tables that are joined, e.g. <i>user\_teams</i> could fit our situation.
 
-We make a small addition to the <i>models/index.js</i> file to connect teams and users at the code level using the [belongsToMany](https://sequelize.org/master/manual/assocs.html#implementation-3) method.
+We make a small addition to the <i>models/index.js</i> file to connect teams and users at the code level using the [belongsToMany](https://sequelize.org/docs/v6/core-concepts/assocs/#implementation-2) method.
 
 ```js
 const Note = require('./note')
@@ -1150,7 +1150,7 @@ For example, the information could be in the following form:
 }
 ```
 
-Note: there are several ways to implement this functionality. [This](https://sequelize.org/master/manual/advanced-many-to-many.html#the-best-of-both-worlds--the-super-many-to-many-relationship) should help.
+Note: there are several ways to implement this functionality. [This](https://sequelize.org/docs/v6/advanced-association-concepts/advanced-many-to-many/#the-best-of-both-worlds-the-super-many-to-many-relationship) should help.
 
 Note also that despite having an array field <i>readinglists</i> in the example, it should always just contain exactly one object, the join table entry that connects the book to the particular user's reading list.
 
@@ -1470,7 +1470,7 @@ Couldn't we optimize the code so that, for example, the model exports the shared
 
 However, the problem is that the definition of the model may change over time, for example the <i>name</i> field may change or its data type may change. Migrations must be able to be performed successfully at any time from start to end, and if the migrations are relying on the model to have certain content, it may no longer be true in a month or a year's time. Therefore, despite the "copy paste", the migration code should be completely separate from the model code.
 
-One solution would be to use Sequelize's [command line tool](https://sequelize.org/master/manual/migrations.html#creating-the-first-model--and-migration-), which generates both models and migration files based on commands given at the command line. For example, the following command would create a <i>User</i> model with <i>name</i>, <i>username</i>, and <i>admin</i> as attributes, as well as the migration that manages the creation of the database table:  
+One solution would be to use Sequelize's [command line tool](https://sequelize.org/docs/v6/other-topics/migrations/#creating-the-first-model-and-migration), which generates both models and migration files based on commands given at the command line. For example, the following command would create a <i>User</i> model with <i>name</i>, <i>username</i>, and <i>admin</i> as attributes, as well as the migration that manages the creation of the database table:  
 
 ```
 npx sequelize-cli model:generate --name User --attributes name:string,username:string,admin:boolean