fixed syntactical errors in HTML code

Fixed HTML Syntactical errors in MiniClaculator.html

Start tag seen without seeing a doctype first. Expected: <!DOCTYPE html>
Saw an end tag after “body” had been closed. Stray end tag “head”.
Element “title” not allowed as child of element “head” in this context [Line 51].
The “frameborder” attribute on the “iframe” element is obsolete. Used CSS instead.

DSCSIT2020 / Hacktoberfest-2020