Update quotes styles in shell script

Using double quotes can be problematic when backslashes are used in the
string.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

cookiecutter/{{cookiecutter.github_repo_name}}/CONTRIBUTING.md

@@ -75,13 +75,14 @@ Here is an example of upgrading the `frequenz-api-common` dependency to version
 `v0.2.0`:
 ```sh
 ver="0.2.0"
+ver_minor=$(echo $ver | cut -d. -f1,2)
 
 cd submodules/frequenz-api-common
 git remote update
 git checkout v${ver}
 cd -
 
-sed s/"frequenz-api-common == [0-9]\.[0-9]\.[0-9]"/"frequenz-api-common == ${ver}"/g -i pyproject.toml
+sed 's/frequenz-api-common == [0-9]\.[0-9]\.[0-9]/frequenz-api-common == '"${ver}/" -i pyproject.toml
 ```
 {%- endif %}