Fix codesign issue on travis macos

https://stackoverflow.com/questions/40994404/xcodebuild-stuck-at-codesign-step-when-being-run-in-travis-ci#41013151

```
I solved same problem by following steps that is described here.

travis-ci/travis-ci#6791 (comment)

a) change argument for all your security imports to keychain from -T to -A

security import ./scripts/certs/dist.cer -k ~/Library/Keychains/ios-build.keychain -A

b) after all imports execute command set-key-partition-list

security set-key-partition-list -S apple-tool:,apple: -s -k <keychainPass> <keychainName>
```

.travis.yml

@@ -48,7 +48,8 @@ matrix:
     - security create-keychain -p mysecretpassword build.keychain
     - security default-keychain -s build.keychain
     - security unlock-keychain -p mysecretpassword build.keychain
-    - security import pibox-installer.p12 -k build.keychain -P $MACOS_CERTIFICATE_PASSWORD -T /usr/bin/codesign
+    - security import pibox-installer.p12 -k build.keychain -P $MACOS_CERTIFICATE_PASSWORD -A
+    - "security set-key-partition-list -S apple-tool:,apple: -s -k -p mysecretpassword build.keychain"
     - security find-identity -v
     - "codesign -s \"Developer ID Application: Wikimedia CH (L7HWM3SP3L)\" dist/pibox-installer.app --deep"