Spring Fix typo in URI Encoding section of reference docs

EncodingMode enum has constant URI_COMPONENT, but documentation uses URI_COMPONENTS.

Comment From: floftar

Relevant source files: - https://github.com/spring-projects/spring-framework/blob/master/spring-web/src/main/java/org/springframework/web/util/DefaultUriBuilderFactory.java - https://github.com/spring-projects/spring-framework/blob/master/spring-web/src/main/java/org/springframework/web/client/RestTemplate.java