Update .travis.yml

Author: jamesmblair

.travis.yml

@@ -5,7 +5,7 @@ install:
   - nuget install xunit.runner.console -Version 2.1.0 -OutputDirectory testrunner
   #- nuget install coveralls.io -Version 1.3.4 -OutputDirectory coveralls
 
-  - $CURRENT_WORKING_DIR=$(pwd)
+  - CURRENT_WORKING_DIR=$(pwd)
 
   - sudo apt-get install gtk-sharp2
   - curl -sS https://api.nuget.org/packages/mono.cecil.0.9.5.4.nupkg > /tmp/mono.cecil.0.9.5.4.nupkg.zip