Docs: fix docker-compose yml volume declarations

This commit adds a yml null `~` as the volume value.
The empty blocks where being interpreted incorrectly by prettier.
This fix was suggested in the related upstream prettier issue.

related: prettier/prettier#4971
closes: prisma/prisma-content-feedback#89
alternative: leonardodino/prisma@c7f35d2

Author: leonardodino

docs/1.0/03-Tutorials/04-Cluster-Deployment/02-Digital-Ocean-(Docker-Machine).md

@@ -145,7 +145,7 @@ networks:
     driver: bridge
 
 volumes:
-  db-persistence:
+  db-persistence: ~
 ```
 
 In `.env`, replace `SECRET_1` and `SECRET_2` (occurs twice) with a long and secure random string.

docs/1.1/03-Tutorials/04-Cluster-Deployment/01-Digital-Ocean-(Docker-Machine).md

@@ -182,7 +182,7 @@ networks:
     driver: bridge
 
 volumes:
-  db-persistence:
+  db-persistence: ~
 ```
 
 </Instruction>

docs/1.1/04-Reference/05-Clusters/02-Docker.md

@@ -83,7 +83,7 @@ networks:
     driver: bridge
 
 volumes:
-  db-persistence:
+  db-persistence: ~
 ```
 
 > **Note**: In an upcoming release, [`prisma-database` will be renamed to just `prisma`](https://github.com/graphcool/prisma/issues/1791).

docs/1.10/03-Tutorials2/01-Setup-Prisma/02-Create-New-DB/01-MySQL.md

@@ -109,7 +109,7 @@ services:
     volumes:
       - mysql:/var/lib/mysql
 volumes:
-  mysql:
+  mysql: ~
 ```
 
 </Instruction>

docs/1.10/03-Tutorials2/01-Setup-Prisma/02-Create-New-DB/02-Postgres.md

@@ -110,7 +110,7 @@ services:
     volumes:
       - postgres:/var/lib/postgresql/data
 volumes:
-  postgres:
+  postgres: ~
 ```
 
 </Instruction>

docs/1.10/03-Tutorials2/06-Deploy-Prisma-Servers/01-Digital-Ocean-(Docker-Machine).md

@@ -186,7 +186,7 @@ networks:
     driver: bridge
 
 volumes:
-  db-persistence:
+  db-persistence: ~
 ```
 
 </Instruction>

docs/1.10/04-Reference/05-Prisma-Servers-&-DBs/02-Database-Connectors/02-MySQL.md

@@ -37,7 +37,7 @@ services:
     volumes:
       - mysql:/var/lib/mysql
 volumes:
-  mysql:
+  mysql: ~
 ```
 
 ## Get started

docs/1.10/04-Reference/05-Prisma-Servers-&-DBs/02-Database-Connectors/03-Postgres.md

@@ -38,7 +38,7 @@ services:
     volumes:
       - postgres:/var/lib/postgresql/data
 volumes:
-  postgres:
+  postgres: ~
 ```
 
 ## Get started

docs/1.11/03-Tutorials2/01-Setup-Prisma/02-Create-New-DB/01-MySQL.md

@@ -109,7 +109,7 @@ services:
     volumes:
       - mysql:/var/lib/mysql
 volumes:
-  mysql:
+  mysql: ~
 ```
 
 </Instruction>

docs/1.11/03-Tutorials2/01-Setup-Prisma/02-Create-New-DB/02-Postgres.md

@@ -110,7 +110,7 @@ services:
     volumes:
       - postgres:/var/lib/postgresql/data
 volumes:
-  postgres:
+  postgres: ~
 ```
 
 </Instruction>