compile with -fPIC and bump cmake version

This couldn't be cherry-picked because but essentially the same change
from the ros2 branch here:
tylerjw@d8d1606

Fixes this error:

```
/usr/bin/ld: /home/alex/ros/h/robotiq/install/serial/lib/libserial.a(serial.cc.o): relocation R_X86_64_PC32 against symbol `_ZTVN6serial6SerialE' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value
```

Signed-off-by: Alex Moriarty <[email protected]>

Author: moriarty

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8.3)
+cmake_minimum_required(VERSION 2.8.12)
 project(serial)
 
 if(APPLE)
@@ -28,6 +28,9 @@ endif()
 
 ## Add serial library
 add_library(${PROJECT_NAME} ${serial_SRCS})
+set_target_properties(${PROJECT_NAME} PROPERTIES
+    POSITION_INDEPENDENT_CODE ON)
+
 if(APPLE)
     target_link_libraries(${PROJECT_NAME} ${FOUNDATION_LIBRARY} ${IOKIT_LIBRARY})
 elseif(UNIX)