swap order of libgsl dependencies

a recent update to libgsl in jessie-backports causes the backported
version to be preferred. revering the order of the libgsl dependencies
caused the default jessie version to be favoured.
Original: ddc8b4b930606ce4ef785da9278a309039e146b6

lal/debian/control.in

@@ -7,7 +7,7 @@ Build-Depends: bc,
   dh-python,
   less,
   libfftw3-dev,
-  libgsl-dev | libgsl0-dev (>= 1.9),
+  libgsl0-dev (>= 1.9) | libgsl-dev,
   libhdf5-dev,
   liboctave-dev,
   pkg-config,
@@ -41,7 +41,7 @@ Architecture: any
 Depends: ${misc:Depends},
   ${shlibs:Depends},
   libfftw3-dev,
-  libgsl-dev | libgsl0-dev (>= 1.9),
+  libgsl0-dev (>= 1.9) | libgsl-dev,
   libhdf5-dev,
   zlib1g-dev,
   lal (= ${binary:Version})