You have to read errors carefully...
Syntax of legacy character encoding declaration:
The string text/html;, optionally followed by whitespace,
followed by charset=,
followed by a preferred encoding name according to the Encoding Standard.
Example: text/html; charset=utf-8
What the validation want is add charset=utf-8 (or other encoding) to your meta, like this:
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
You also should check this validation service:
http://validator.w3.org/[
^]