uri: fix uri.c generation command (make ragel)

The bug was introduced in d735b6bf (move
'uri' lib to src/lib/).

src/lib/uri/CMakeLists.txt

 add_custom_target(ragel
     WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
-    COMMAND ragel -G2 src/uri.rl -o src/uri.c)
+    COMMAND ragel -G2 src/lib/uri/uri.rl -o src/lib/uri/uri.c)
 
 if (CC_HAS_WNO_IMPLICIT_FALLTHROUGH)
     # Suppress noise warnings for autogenerated Ragel code