Fix checklist typo and use a consistent number of spaces around headings.

I noticed this while filling out the checklist for #183

Author: BillyONeal

.github/pull_request_template.md

@@ -3,7 +3,7 @@
  - I have read the [contribution guidelines](../CONTRIBUTING.md).
  - I have updated the documentation, if applicable.
  - I have ensured that the change is tested somewhere.
- - I have followed the prevailing code style (for history readability and limit conflicts for maintainance).
+ - I have followed the prevailing code style (for history readability and limit conflicts for maintenance).
 
 -->
 ## Description
@@ -19,10 +19,8 @@
 - [X] Add "X" when it is done.
 -->
 
-
 ## Implementation remarks
 
-
 <!--
 Explain main implementation choices.
 It is also the right place to ask for feedback and help when you hesitate on the implementation.