Fix the Travis manual compiling script (#664)

Author: thisrod

docs/travis.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
 if [ ${TRAVIS_OS_NAME} = "linux" ]; then
-    julia -e 'Pkg.add("Documenter")';
-    julia -e 'cd(Pkg.dir("ApproxFun")); include(joinpath("docs", "make.jl"))';
+    julia -e 'using Pkg; Pkg.add("Documenter")';
+    julia -e 'using Pkg; cd(Pkg.dir("ApproxFun")); include(joinpath("docs", "make.jl"))';
 fi