Update GSON dependency (#19)

README.md

@@ -118,7 +118,7 @@ dependencies {
 * Run ```gradle build``` in the root directory of the repository
 
 ### Creating a test Harvest account
-Go to https://www.getharvest.com/signup
+Go to [Harvest Sign up](https://www.getharvest.com/signup)
 - Use your 3ap email with a "+<month><year>" added to the name, e.g. marco+Jul2020@3ap.ch (this way you can create a filter in gmail to archive the emails you get)
 - Choose "Me and my team"
 - Select "Next Step" until the end.

build.gradle

@@ -165,11 +165,12 @@ dependencies {
     testImplementation group: "org.apache.logging.log4j", name: "log4j-slf4j-impl", version: "$log4jVersion"
 
     // immutable classes for domain objects
-    // this will force gson 2.8 also for other dependencies
     implementation "org.immutables:gson:$immutablesVersion"
     compileOnly "org.immutables:value:$immutablesVersion"
     annotationProcessor "org.immutables:value:$immutablesVersion"
 
+    implementation "com.google.code.gson:gson:$gsonVersion"
+
     implementation group: "com.google.code.findbugs", name: "jsr305", version: "3.0.2"
 
     // configuration

gradle.properties

@@ -2,7 +2,8 @@
 retrofitVersion=2.3.0
 junitVersion=5.1.0
 log4jVersion=2.14.1
-immutablesVersion=2.5.6
+immutablesVersion=2.8.8
+gsonVersion=2.8.9
 okhttpVersion=3.10.0
 slf4jVersion=1.7.32
 # Signing configuration. Empty means it has to be set for a release