Merge pull request #215 from WPH95/update_okhttp_version

fix bug: com.qiniu.http.Client throw NullPointerException

Author: longbai

build.gradle

@@ -18,7 +18,7 @@ dependencies {
 //    if (c < 0) {
 //        compile fileTree(dir: 'libs', include: '*.jar')
 //    } else {
-    compile group:'com.squareup.okhttp3', name:'okhttp', version:'3.2.0'
+    compile group:'com.squareup.okhttp3', name:'okhttp', version:'3.3.1'
 //    }
     compile group:'com.google.code.gson', name:'gson', version:'2.6.2'
     testCompile group: 'junit', name: 'junit', version: '4.12'