Use gradle 2.7 in builds.

Reviewed at https://reviews.apache.org/r/39113/
diff --git a/builder/deb/ubuntu-trusty/Dockerfile b/builder/deb/ubuntu-trusty/Dockerfile
index a827c7a..9f0257d 100644
--- a/builder/deb/ubuntu-trusty/Dockerfile
+++ b/builder/deb/ubuntu-trusty/Dockerfile
@@ -44,8 +44,8 @@
 RUN git clone --depth 1 https://github.com/benley/gradle-packaging \
   && cd gradle-packaging \
   && apt-get install -y ruby ruby-dev unzip wget \
-  && gem install fpm && ./gradle-mkdeb.sh 2.6 \
-  && dpkg -i gradle-2.6_2.6-2_all.deb \
+  && gem install fpm && ./gradle-mkdeb.sh 2.7 \
+  && dpkg -i gradle-2.7_2.7-2_all.deb \
   && cd .. && rm -rf gradle-packaging
 
 ADD build.sh /build.sh
diff --git a/specs/debian/control b/specs/debian/control
index b286517..4aa6bf3 100644
--- a/specs/debian/control
+++ b/specs/debian/control
@@ -3,7 +3,7 @@
 Maintainer: The Apache Aurora authors <dev@aurora.apache.org>
 Build-Depends: debhelper (>= 9),
  java8-sdk | openjdk-8-jdk,
- gradle (>= 2.6) | gradle-2.6,
+ gradle (>= 2.7) | gradle-2.7,
  python-all-dev,
  libkrb5-dev,
  curl,
diff --git a/specs/rpm/aurora.spec b/specs/rpm/aurora.spec
index cf9c271..944c1c0 100644
--- a/specs/rpm/aurora.spec
+++ b/specs/rpm/aurora.spec
@@ -30,7 +30,7 @@
 %endif
 
 %if %{?!GRADLE_VERSION:1}0
-%global GRADLE_VERSION 2.6
+%global GRADLE_VERSION 2.7
 %endif
 
 %if %{?!JAVA_VERSION:!}0