Use `https` for npmjs.org.
Losslessly compress PNG files.

Before: 306 KB (313.883 bytes)
After:  244 KB (250.632 bytes)
Update README.md
Fix mistake
Add devDependencies to profile
Merge pull request #168 from aivus/readme_fix

Update README.md
Merge pull request #162 from XhmikosR/fix-155

Use `https` for npmjs.org.
Merge pull request #163 from XhmikosR/img-compression

Losslessly compress PNG files.
Merge pull request #169 from leecrossley/master

Add devDependencies to profile
Minor JS tweaks found with ESLint.