If you have a medium-large site using both jekyll-mentions and jemoji, then you can shave a couple of seconds from the total build time by using jekyll-mentioji instead.
Its a bit faster yet fully compatible with existing configuration settings for the two plugins.
Cheers 
Disclaimer: Not whitelisted for use with github-pages gem
I have used jemoji in one of my blogs and it has converted all of my emoji into images.
@yashumittal I’m sorry, but what are you trying to say…?
I mean that jemoji plugin is not working for my blog site, as it is converting all the emoji into images.
That is exactly what the jemoji plugin is designed for: To convert text :smiley: into a 
graphic!!
The issue with your post is purely CSS related.
Open your browser’s Inspector tool and disable the following CSS Rule to preview your intended rendering:
.article img {
/* width: 100%; */
height: auto;
border-radius: 6px;
box-shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.15);
}
While your CSS is technically correct, the parent container is too fluid to actually “constrain” the generated images to an acceptable width n height.
It is converting into .png images, didn’t you checked the blog link I have posted.
Shouldn’t it be just emoji (instead of converted into .png or .jpg)