modify java sdk version to 2.7.0 (#202)

Author: cyjseagull

build.gradle

@@ -36,7 +36,7 @@ ext {
 // integrationTest.mustRunAfter test
 allprojects {
     group = 'org.fisco-bcos.java-sdk'
-    version = '2.7.0-SNAPSHOT'
+    version = '2.7.0'
     apply plugin: 'maven'
     apply plugin: 'maven-publish'
     apply plugin: 'idea'