Add some more rules to dangerfile (#1560)

* warn if the target branch is not master
* link to the logo guidance if PR modifies a SVG file in /logo/

dangerfile.js

@@ -23,17 +23,27 @@ const helpers = fileMatch(
   '!**/*.spec.js',
   '!lib/all-badge-examples.js'
 );
+const logos = fileMatch(
+  'logo/*.svg'
+);
 const helperTests = fileMatch('lib/**/*.spec.js');
 const packageJson = fileMatch('package.json');
 const packageLock = fileMatch('package-lock.json');
 const capitals = fileMatch('**/*[A-Z]*.js');
 const underscores = fileMatch('**/*_*.js');
+const targetBranch = danger.github.pr.base.ref;
 
 message([
   ':sparkles: Thanks for your contribution to Shields, ',
   `@${danger.github.pr.user.login}!`
 ].join(''));
 
+if (targetBranch != 'master') {
+  const message = `This PR targets \`${targetBranch}\``;
+  const idea = 'It is likely that the target branch should be `master`';
+  warn(`${message} - <i>${idea}</i>`);
+}
+
 if (documentation.createdOrModified) {
   message([
     'Thanks for contributing to our documentation. ',
@@ -66,6 +76,15 @@ if (helpers.created && !helperTests.created) {
   ].join(''));
 }
 
+if (logos.created) {
+  message([
+    ':art: Thanks for submitting a logo. ',
+    'Please ensure your contribution follows our ',
+    '[guidance](https://github.com/badges/shields/blob/master/CONTRIBUTING.md#logos) ',
+    'for logo submissions.'
+  ].join(''));
+}
+
 if (capitals.created || underscores.created) {
   fail([
     'JavaScript source files should be named with kebab-case ',