Explicitly depend on Python 2.7

Not using a more specific binary causes build failures on systems where
the default Python is 3. The existing backends, angr and Manticore, both
require Python 2.7, so we can look at supporting Python 3 when they do.

CMakeLists.txt

@@ -30,7 +30,7 @@ set(CMAKE_C_FLAGS_RELEASE "-O3")
 set(CMAKE_CXX_FLAGS_DEBUG "-O3")
 set(CMAKE_CXX_FLAGS_RELEASE "-O3")
 
-find_program(PYTHON "python")
+find_program(PYTHON "python2.7")
 
 # Enable the GNU extensions
 set(CMAKE_CXX_EXTENSIONS ON)
@@ -64,7 +64,7 @@ target_include_directories(${PROJECT_NAME}32
   PUBLIC SYSTEM "${CMAKE_SOURCE_DIR}/src/include"
 )
 
-# Install the 
+# Install the
 install(
   DIRECTORY "${CMAKE_SOURCE_DIR}/src/include/deepstate"
   DESTINATION include