make the i2p version a variable

build.gradle

@@ -2,7 +2,7 @@ subprojects {
     apply plugin: 'groovy'
 
     dependencies {
-        compile 'net.i2p:i2p:0.9.42'
+        compile "net.i2p:i2p:${i2pVersion}"
         compile 'org.codehaus.groovy:groovy-all:2.4.15'
     }
 

core/build.gradle

@@ -2,9 +2,9 @@ apply plugin : 'application'
 mainClassName = 'com.muwire.core.Core'
 applicationDefaultJvmArgs = ['-Djava.util.logging.config.file=logging.properties']
 dependencies {
-    compile 'net.i2p:router:0.9.42'
-    compile 'net.i2p.client:mstreaming:0.9.42'
-    compile 'net.i2p.client:streaming:0.9.42'
+    compile "net.i2p:router:${i2pVersion}"
+    compile "net.i2p.client:mstreaming:${i2pVersion}"
+    compile "net.i2p.client:streaming:${i2pVersion}"
 
     testCompile 'org.junit.jupiter:junit-jupiter-api:5.4.2'    
     testCompile 'junit:junit:4.12'

gradle.properties

@@ -1,5 +1,6 @@
 group         = com.muwire
 version       = 0.5.1
+i2pVersion    = 0.9.42
 groovyVersion = 2.4.15
 slf4jVersion  = 1.7.25
 spockVersion  = 1.1-groovy-2.4