upgrade to 2.7.5 snapshot (#123)

diff --git a/.travis.yml b/.travis.yml
index a321125..163f877 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,9 +16,8 @@
 install: true
 
 script:
-  - ./mvnw --batch-mode --no-transfer-progress --settings .mvn/settings.xml clean install -pl dubbo-maven-address-plugin -U
-  - ./mvnw --batch-mode --no-transfer-progress --settings .mvn/settings.xml clean verify -Pdubbo-integration-test -Djava-image.name=${JAVA_BASE_IMAGE} -Ddubbo.version=2.7.4-SNAPSHOT -U
-
+  - ./mvnw -U --batch-mode --no-transfer-progress --settings .mvn/settings.xml clean install -pl dubbo-maven-address-plugin -Ddubbo.version=2.7.5-SNAPSHOT
+  - ./mvnw -U --batch-mode --no-transfer-progress --settings .mvn/settings.xml clean verify -Pdubbo-integration-test -Djava-image.name=${JAVA_BASE_IMAGE} -Ddubbo.version=2.7.5-SNAPSHOT
 
 after_success:
   - bash <(curl -s https://codecov.io/bash)