Remove Nuget package install from apt-get in Travis.

We're getting an error installing the package E: Unable to locate package nuget

.travis.yml

@@ -17,7 +17,7 @@ install:
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then echo "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list; fi
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then echo "deb http://download.mono-project.com/repo/debian wheezy-libtiff-compat main" | sudo tee -a /etc/apt/sources.list.d/mono-xamarin.list; fi
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then sudo apt-get update -qq; fi
-  - if [ "$TRAVIS_OS_NAME" = "linux" ]; then sudo apt-get install -y mono-devel nuget p7zip-full; fi
+  - if [ "$TRAVIS_OS_NAME" = "linux" ]; then sudo apt-get install -y mono-devel p7zip-full; fi
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then brew install wget p7zip; fi
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then wget -O mono.pkg http://download.mono-project.com/archive/nightly/macos-10-x86/mono-MDK.pkg; fi
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then sudo installer -pkg "mono.pkg" -target /; fi