Adding test scenarios for displaying exported variables

This commit includes two file updates for testing the new feature
as requested in jamesob#56. The example hello deskfile now has
a variable set called MyName with a value "James" and the runtests
shell script includes a test to echo the value of that variable.

This test proves that the variable is exported as expected from the
deskfile and is retrievable as expected.

Still #todo includes a test that lists the description of the deskfile
and looks for that variable to be listed along with the aliases and
functions.

examples/hello.sh

@@ -9,3 +9,6 @@ hi() {
 # Use if you're from Texas. 
 alias howdy="echo howdy y\'all"
 
+# Why should I always type my name
+export MyName="James"
+

test/run_tests.sh

@@ -129,6 +129,10 @@ RAN=$(desk run hello 'hi j')
 echo "$RAN" | grep 'hi, j!' >/dev/null
 ensure $? "Run in desk 'hello' didn't work with hi function"
 
+RAN=$(desk run hello 'echo $MyName')
+echo "$RAN" | grep 'James' >/dev/null
+ensure $? "Run in desk 'hello' didn't work with MyName exported variable"
+
 ## `desk go`
 
 RAN=$(desk go example-project/Deskfile -c 'desk ; exit')