Updated build configuration to version 3.1.0

Author: jyemin

build.gradle

@@ -45,7 +45,7 @@ configure(subprojects.findAll { it.name != 'util' }) {
     evaluationDependsOn(':util')
 
     group = 'org.mongodb'
-    version = '3.1.0-SNAPSHOT'
+    version = '3.1.0'
     sourceCompatibility = JavaVersion.VERSION_1_6
     targetCompatibility = JavaVersion.VERSION_1_6