Correction to swig detection with cmake
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0d4ee74..37e8c72 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -66,9 +66,13 @@
 
 find_package(SWIG)
 
-if(NOT SWIG_FOUND)
-    message(FATAL_ERROR "SWIG required to compile gr-gsm")
-endif()
+if(SWIG_FOUND)
+    # Minimum SWIG version required is 1.3.31
+    set(SWIG_VERSION_CHECK FALSE)
+    if("${SWIG_VERSION}" VERSION_GREATER "1.3.30")
+        set(SWIG_VERSION_CHECK TRUE)
+    endif()
+endif(SWIG_FOUND)
 
 
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