Update translations

[EvanHerman]

WPCS isn't a fan of our translation strings and is throwing an error.

https://travis-ci.org/godaddy/wp-primer-theme/jobs/216079486

We should update our strings to reflect the following format:

<?php
/* translators: %s: post title */
printf( esc_attr__( 'Continue reading %s', 'primer' ), get_the_title() ); 
?>

In a recent discussion with a core translator I was informed that _x functions are used for multiple instances of the same word(s) to add context.

Not sure how this approach would effect the current method of translating, but something that needs to be addressed.