Update README.md for retrofit-converters (square#2996)

* fix broken link

* adding link for guava

* modify incorrect link

* modify incorrect link

* fix broken link

retrofit-converters/guava/README.md

@@ -1,30 +1,30 @@
 Guava Converter
 ===============
 
-A `Converter` which supports Guava's `Optional<T>` by delegating to other converters for `T`
+A `Converter` which supports [Guava][1]'s `Optional<T>` by delegating to other converters for `T`
 and then wrapping it into `Optional`.
 
 
 Download
 --------
 
-Download [the latest JAR][1] or grab via [Maven][2]:
+Download [the latest JAR][2] or grab via [Maven][3]:
 ```xml
 <dependency>
   <groupId>com.squareup.retrofit2</groupId>
   <artifactId>converter-guava</artifactId>
   <version>latest.version</version>
 </dependency>
 ```
-or [Gradle][2]:
+or [Gradle][3]:
 ```groovy
 implementation 'com.squareup.retrofit2:converter-guava:latest.version'
 ```
 
 Snapshots of the development version are available in [Sonatype's `snapshots` repository][snap].
 
 
-
- [1]: https://search.maven.org/remote_content?g=com.squareup.retrofit2&a=converter-guava&v=LATEST
- [2]: http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.squareup.retrofit2%22%20a%3A%22converter-guava%22
+ [1]: https://github.com/google/guava
+ [2]: https://search.maven.org/remote_content?g=com.squareup.retrofit2&a=converter-guava&v=LATEST
+ [3]: http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.squareup.retrofit2%22%20a%3A%22converter-guava%22
  [snap]: https://oss.sonatype.org/content/repositories/snapshots/

retrofit-converters/jackson/README.md

@@ -27,7 +27,8 @@ Snapshots of the development version are available in [Sonatype's `snapshots` re
 
 
 
- [1]: http://wiki.fasterxml.com/JacksonHome
+ [1]: https://github.com/FasterXML/jackson
  [2]: https://search.maven.org/remote_content?g=com.squareup.retrofit2&a=converter-jackson&v=LATEST
  [3]: http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.squareup.retrofit2%22%20a%3A%22converter-jackson%22
  [snap]: https://oss.sonatype.org/content/repositories/snapshots/
+