You can use display:table and display:table-cell property.
Vertically centered text
HTML:
<footer>
  <p>Copyright 2016 - Say my name. All Rights Reserved</p>
</footer>
CSS:
footer {
  display: table;
  position: relative;
  height: 15vh;
  width: 100vw;
  background: #1a1a1a;
  border-top: 1px solid #232323;
  color: #a0a0a0;
  padding-left: 5%;
  box-sizing: border-box;
}
footer p {
  display: table-cell;
  vertical-align: middle;
  line-height: 1vh;
}
footer {
  display: table;
  position: relative;
  height: 15vh;
  width: 100vw;
  background: #1a1a1a;
  border-top: 1px solid #232323;
  color: #a0a0a0;
  padding-left: 5%;
  box-sizing: border-box;
}
footer p {
  display: table-cell;
  vertical-align: middle;
  line-height: 1vh;
}
<footer>
  <p>Copyright 2016 - Say my name. All Rights Reserved</p>
</footer>
 
 
Or you can use flex property,but its not supported by many browser version
Align using flex property
CSS:
footer {
  display: flex;
  justify-content: center;        /* align horizontal */
  align-items: center;        /*ALIGN VERTICAL*/
  position: relative;
  height: 15vh;
  width: 100vw;
  background: #1a1a1a;
  border-top: 1px solid #232323;
  color: #a0a0a0;
  padding-left: 5%;
  box-sizing: border-box;
}
footer p {  
   line-height: 1vh;
}
footer {
  display: flex;
  justify-content: center;        /* align horizontal */
  align-items: center;        /*ALIGN VERTICAL*/
  position: relative;
  height: 15vh;
  width: 100vw;
  background: #1a1a1a;
  border-top: 1px solid #232323;
  color: #a0a0a0;
  padding-left: 5%;
  box-sizing: border-box;
}
footer p {
  
  vertical-align: middle;
  line-height: 1vh;
}
<footer>
  <p>Copyright 2016 - Say my name. All Rights Reserved</p>
</footer>