Run pod linter for one Travis configuration (#33)

* run pod linter for one of the Travis configurations
* use more recent CocoaPods on Travis for pod linting

.travis.yml

@@ -1,8 +1,5 @@
 language: objective-c
 
-install:
- - gem install xcpretty
-
 env:
  global:
  - LC_CTYPE=en_US.UTF-8
@@ -16,7 +13,7 @@ matrix:
  - osx_image: xcode10.1
  env: SCHEME="macOS" SDK="macosx10.14" DESTINATION="arch=x86_64" SWIFT_VERSION="4.2" ACTION="test"
  - osx_image: xcode10.2
- env: SCHEME="macOS" SDK="macosx10.14" DESTINATION="arch=x86_64" SWIFT_VERSION="5.0" ACTION="test"
+ env: SCHEME="macOS" SDK="macosx10.14" DESTINATION="arch=x86_64" SWIFT_VERSION="5.0" ACTION="test" POD_LINT="YES"
  - osx_image: xcode10.2
  env: SCHEME="iOS" SDK="iphonesimulator" DESTINATION="OS=12.0,name=iPhone 8" SWIFT_VERSION="5.0" ACTION="test"
  - osx_image: xcode10.2
@@ -25,8 +22,15 @@ matrix:
  env: SCHEME="watchOS" SDK="watchsimulator" DESTINATION="OS=4.0,name=Apple Watch - 42mm" SWIFT_VERSION="5.0" ACTION="build"
 
 before_install:
+ - if [ $POD_LINT == "YES" ]; then
+ gem install cocoapods -v '1.7.5';
+ pod repo update;
+ fi
  - carthage bootstrap --platform "$SCHEME" --verbose
 
+install:
+ - gem install xcpretty
+
 script:
  - set -o pipefail
  - xcodebuild -version
@@ -42,6 +46,9 @@ script:
  GCC_INSTRUMENT_PROGRAM_FLOW_ARCS=YES
  GCC_GENERATE_TEST_COVERAGE_FILES=YES
  SWIFT_VERSION=$SWIFT_VERSION
+ - if [ $POD_LINT == "YES" ]; then
+ pod lib lint --verbose;
+ fi
 
 after_success:
  - bash <(curl -s https://codecov.io/bash) -J ReSwift-Thunk