build: Update 'svgo' and add 'minify:svg' SVGO icons build step

We're already using 'svgo', but we currently feature no npm build step
with Wikimedia's adhered SVG guidelines.
Not yet adding minification to 'build:svg' step as long as we're
clarifying optimization output differences between SVGO versions.

Change-Id: Iec5845e238a61e3b1a86f8cf4f0272a2c2acfe23