add isMagnetURI #877

[Adibla]

Add simple function/test to validate magnet URI string

[chriso]

Thanks for the PR 😄

Do you mind adding an entry to the README?

[chriso]

Can you fix the lint errors?

/home/travis/build/chriso/validator.js/src/lib/isMagnetURI.js
  1:1  error  Expected 1 empty line after import statement not followed by another import  import/newline-after-import
  5:1  error  Expected indentation of 2 spaces but found 4                                 indent
  6:1  error  Expected indentation of 2 spaces but found 4                                 indent
/home/travis/build/chriso/validator.js/test/validators.js
  5631:1  error  More than 2 blank lines not allowed  no-multiple-empty-lines
  5632:1  error  Trailing spaces not allowed          no-trailing-spaces

[chriso]

Thanks!