[ fix ] use spaces, not tabs in .travis.yml

Author: gallais

.travis.yml

@@ -112,8 +112,8 @@ matrix:
         # setting up travis-specific scripts and files
         - cp travis/* .
 
-	# create a suitable Agda `executables` file for examples in README using `Reflection.External`
-	- echo -e "/usr/bin/expr\n" ~/.agda/executables
+        # create a suitable Agda `executables` file for examples in README using `Reflection.External`
+        - echo -e "/usr/bin/expr\n" ~/.agda/executables
 
       before_script:
         - export AGDA_OPTIONS="-Werror"