replace warning emoji with warning unicode (#317)

Due to the use of the emoji, the documentation page shows
:warning: instead of ⚠.
https://cordova.apache.org/docs/en/latest/reference/cordova-plugin-camera/index.html

README.md

@@ -57,7 +57,7 @@ Contributors are welcome! And we need your contributions to keep the project mov
 
 There is a specific [contributor workflow](http://wiki.apache.org/cordova/ContributorWorkflow) we recommend. Start reading there. More information is available on [our wiki](http://wiki.apache.org/cordova).
 
-:warning: **Found an issue?** File it on [JIRA issue tracker](https://issues.apache.org/jira/issues/?jql=project%20%3D%20CB%20AND%20status%20in%20(Open%2C%20%22In%20Progress%22%2C%20Reopened)%20AND%20resolution%20%3D%20Unresolved%20AND%20component%20%3D%20%22cordova-plugin-camera%22%20ORDER%20BY%20priority%20DESC%2C%20summary%20ASC%2C%20updatedDate%20DESC).
+⚠ **Found an issue?** File it on [JIRA issue tracker](https://issues.apache.org/jira/issues/?jql=project%20%3D%20CB%20AND%20status%20in%20(Open%2C%20%22In%20Progress%22%2C%20Reopened)%20AND%20resolution%20%3D%20Unresolved%20AND%20component%20%3D%20%22cordova-plugin-camera%22%20ORDER%20BY%20priority%20DESC%2C%20summary%20ASC%2C%20updatedDate%20DESC).
 
 **Have a solution?** Send a [Pull Request](https://github.com/apache/cordova-plugin-camera/pulls).
 
@@ -68,7 +68,7 @@ In order for your changes to be accepted, you need to sign and submit an Apache
 
 ## This documentation is generated by a tool
 
-:warning: Run `npm install` in the plugin repo to enable automatic docs generation if you plan to send a PR.  
+⚠ Run `npm install` in the plugin repo to enable automatic docs generation if you plan to send a PR.  
 [jsdoc-to-markdown](https://www.npmjs.com/package/jsdoc-to-markdown) is used to generate the docs.  
 Documentation consists of template and API docs produced from the plugin JS code and should be regenerated before each commit (done automatically via [husky](https://github.com/typicode/husky), running `npm run gen-docs` script as a `precommit` hook - see `package.json` for details).