Icon font uses an incorrect "appendUniconde" option

[recrit]

Issue
The "appendUniconde" is spelled wrong and should have been "appendUnicode", so it was never being used anyways.
The new option for "gulp-svgicons2svgfont" is "prependUnicode", see changes in nfroidure/gulp-svgicons2svgfont#33.

See https://github.com/nfroidure/gulp-svgicons2svgfont
"
options.prependUnicode
Type: Boolean Default value: false

Allow to prepend unicode codepoints to icon file names in order to always keep the same codepoints accross each run
"

This leads to inconsistent codepoints on subsequent builds which leads to incorrect icons displayed for browsers thats really like to cache icon files even with a cache bust query string.

Affected Versions
All versions.

[recrit]

The PR #57 is for the 9.x version but this needs fixed in all versions.