Add Travis CI and fix an analyze issue

.travis.yml

@@ -0,0 +1,20 @@
+language: dart
+dist: bionic
+addons:
+  apt:
+    packages:
+      - lib32stdc++6
+install:
+  - git clone https://github.com/flutter/flutter.git -b stable --depth 1
+  - export PATH=./flutter/bin:$PATH
+  - flutter doctor --version
+script:
+  - cd $TRAVIS_BUILD_DIR
+  - flutter pub get
+  - flutter pub upgrade
+  - flutter packages pub run build_runner build --delete-conflicting-outputs
+  - flutter analyze --no-pub --no-current-package lib/
+  - flutter build apk
+cache:
+  directories:
+    - $HOME/.pub-cache

lib/ui/views/history_view.dart

@@ -144,6 +144,7 @@ class HistoryView extends StatelessWidget {
               iconColor: blueColor,
               tapHeaderToExpand: true),
           child: ExpandablePanel(
+            collapsed: Container(),
             header: InkWell(
                 child: Text(
               paste.id,