Changed space of + into proper url code

[Razikus]

Obviously a bug
%20 is space

[pablogalegoc]

Hello @stevespringett! Do you think this PR could be merged? It's a very simple change and without it we can't rely on the equality check with pURLs generated by this library. Thank you in advance and thank you @Razikus for opening it.

[stevespringett]

Thanks for the PR. Looks like unit tests are failing.
https://app.travis-ci.com/github/package-url/packageurl-java/builds/260013012

[pablogalegoc]

Indeed, after looking at the failing test I believe the issue is a bit more complex than just substituting "%20" for "%2B".
According to the spec, a pURL is a URL that conforms to RFC 3986 (1). However, the current implementation is not encoding in conformance with RFC 3986 because of URLEncoder:

packageurl-java/src/main/java/com/github/packageurl/PackageURL.java

Lines 429 to 441 in bd3241a

	* Encodes the input in conformance with RFC 3986.
	*
	* @param input the String to encode
	* @return an encoded String
	*/
	private String percentEncode(final String input) {
	try {
	return URLEncoder.encode(input, UTF8)
	.replace("+", "%20")
	// "*" is a reserved character in RFC 3986.
	.replace("*", "%2A")
	// "~" is an unreserved character in RFC 3986.
	.replace("%7E", "~");

URLEncoder doesn't mention any RFC in the documentation and makes some substitutions (like "+" for " ") that are the cause of those .replace() calls. I'm not aware of a standard library class for Java 8 that encodes a string following RFC 3986, but we can take inspiration from Spring's UriUtils for a simple implementation.

@Razikus do you think you can take a look at this? I can do it if you don't have the time 🙂

[stevespringett]

Closing as resolved and fixed with #98