Update .travis.yml

Author: AdityaMulgundkar

.travis.yml

@@ -23,7 +23,7 @@ matrix:
             jdk: oraclejdk8
             sudo: false
             addons: {apt: {sources: [ubuntu-toolchain-r-test], packages: [libstdc++6, fonts-droid]}}
-            before_script: ['wget http://services.gradle.org/distributions/gradle-3.5-bin.zip', 'unzip -qq gradle-3.5-bin.zip', 'export GRADLE_HOME=$PWD/gradle-3.5', 'export PATH=$GRADLE_HOME/bin:$PATH', 'git clone https://github.com/flutter/flutter.git -b stable']
+            before_script: ['wget https://services.gradle.org/distributions/gradle-3.5-bin.zip', 'unzip -qq gradle-3.5-bin.zip', 'export GRADLE_HOME=$PWD/gradle-3.5', 'export PATH=$GRADLE_HOME/bin:$PATH', 'git clone https://github.com/flutter/flutter.git -b stable']
             script: ['./flutter/bin/flutter -v build apk']
     cache:
         directories: