Fix a README mistake on option SPATIAL_LIBRARY (#13162)

README.md

@@ -294,7 +294,7 @@ Library specific options:
     REDIS_INCLUDE_DIR               - Only when building with Redis; directory that contains hiredis.h
     REDIS_LIBRARY                   - Only when building with Redis; path to libhiredis.a/libhiredis.so
     SPATIAL_INCLUDE_DIR             - Only when building with LibSpatial; directory that contains spatialindex/SpatialIndex.h
-    SPATIAL_LIBRARY                 - Only when building with LibSpatial; path to libspatialindex_c.so/spatialindex-32.lib
+    SPATIAL_LIBRARY                 - Only when building with LibSpatial; path to libspatialindex.so/spatialindex-32.lib
     LUA_INCLUDE_DIR                 - Only if you want to use LuaJIT; directory where luajit.h is located
     LUA_LIBRARY                     - Only if you want to use LuaJIT; path to libluajit.a/libluajit.so
     OGG_DLL                         - Only if building with sound on Windows; path to libogg.dll