title: Can not install php-mbstring on centOS
body: <p>I had php 5.4 on centOs and I have removed that and installed php 7.
  Now One of my codes on server return the following error:</p>
  <blockquote>
  <p>PHP Fatal error:  Call to undefined function mb_internal_encoding()</p>
  </blockquote>
  <p>And when I run <code>yum install php-mbstring</code> I got the following error:</p>
  <blockquote>
  <p>Error: php70u-common conflicts with php-common-5.4.16-43.el7_4.x86_64</p>
  <p>Error: php70u-json conflicts with php-common-5.4.16-43.el7_4.x86_64</p>
  </blockquote>
  <p>I have removed and installed php7 several times but I didn't work.
  It seems that centOs want to install an older version of the package but I don't know how to tell it to download the latest version of mbstring</p>