Changed html, css, js, md and text file icons

[leodev12345]

Requirements (please check off with 'x')

• I have read the Contributing Guidelines
• I have read or at least glanced at the FAQ
• I have read or at least glanced at the Wiki

What does this Pull Request (PR) do?

I have changed:

• html and htm icon from <> to html 5 icon
• slim and haml icons from <> to their logos
• css # icon to css3 icon
• javascript JS icon to the javascript logo icon
• less icon from # to less logo
• mjs icon from JS to node.js icon
• markdown icon from arrow pointing down to md logo
• changed icons for .gitignore, .gitattributes and .gitconfig to git logo
• added icon for .gitmodules (git logo)
• default text icon from the paragraph of text to a text box icon, personally i think it looks more like a file icon for a text file

How should this be manually tested?

By installing my fork of vim-devicons into vim, you can see the icons in NERDtree and airline tabs

Any background context you can provide?

These icons are just my personal preference so I don't know if they will make it into official vim-devicons
I think html5 and css3 is used pretty much all the time now so I dont see the point of having the old icons
Sorry if I didn't do something right this is my first time ever writing a PR

Screenshots (if appropriate or helpful)

You can see the updated html, css, and js icons in the NERDtree in this screenshot:

Example of new default text file icon:

Example of new md icon:

Example of new git icon:

[marslo]

can you please help also enable gitcommit for .git/COMMIT_EDITMSG as well ?
i.e.:

$ git commit --amend

---- edit ----
Okay, never mind, I've added the gitcommit into #459
please let me know if you have any concern on this.