Fixing typo

I believe it is supposed to be written this way.
Adding missing verb
Fixing small bits in the portuguese translations
Grammar and English idioms restructuring.
Update performance-matters.html.md
Update performance-matters.html.md
Update performance-matters.html.md
Update avoid-inline.html.md
Update css-on-top-js-on-bottom.html.md
Update compress.html.md
Update css-on-top-js-on-bottom.html.md
Update async.html.md
Update combine-css.html.md
Update minify-css.html.md
Update prefer-link-over-import.html.md
Update data-uri.html.md

Cambié "estamus" por "estamos"
Update 3rd-party-async.html.md
Update cache-array-lengths.html.md
Update cache-array-lengths.html.md
Update documentwrite.html.md