Mandatory parameters are escaped twice when using Traverson API

Related to #337 when a rel contains a mandatory param that needs to be escaped, it will be escaped twice.
In the following example, the rel to follow is /springagram/item/{itemId} where itemId is '123#456'

Resource<?> itemResource = traverson.//
    follow(rel("item").withParameters(Collections.singletonMap("itemId", "123#456"))).//
    toObject(Resource.class);

The final url will be resolved as /springagram/item/123%2523456 instead of /springagram/item/123%23456

The problem is inside org.springframework.hateoas.UriTemplate#expand(java.util.Map<java.lang.String,? extends java.lang.Object>)
When creating a new org.springframework.web.util.UriTemplate, the baseUri is escaped a first time (# is escaped as %23).
Then, when executing builder.build().toUri() the whole url is escaped a second time (hence %23 is escaped as %2523).

The thing is that is works well if you only have optional param inside your rel but as soon as you have one mandatiry param that needs to be escaped, then it will be escaped twice.

Start at org.springframework.hateoas.UriTemplate#expand(Map<String, ? extends Object>) and trace how the base URI is passed through org.springframework.web.util.UriTemplate and builder.build().toUri(). Reproduce the Traverson example with itemId "123#456". Done means the final URL contains 123%23456 rather than 123%2523456, while optional parameters continue to work.