feat(config-conventional): increase header-max-length to 100 (conventional-changelog#860)

Closes conventional-changelog#859.

Author: mightyiam

@commitlint/config-conventional/README.md

@@ -125,7 +125,7 @@ echo "fix: some message" # passes
 * **rule**: `always`
 * **value**
 ```js
-  72
+  100
 ```
 
 ```sh

@commitlint/config-conventional/index.js

@@ -3,7 +3,7 @@ module.exports = {
 	rules: {
 		'body-leading-blank': [1, 'always'],
 		'footer-leading-blank': [1, 'always'],
-		'header-max-length': [2, 'always', 72],
+		'header-max-length': [2, 'always', 100],
 		'scope-case': [2, 'always', 'lower-case'],
 		'subject-case': [
 			2,