typo in CMakeLists.txt

Typo in CMakeLists.txt _in the downloaded version_ 0.11.0.tar.gz with md5sum 6fba4f2f64f19af9f172fd60ad8e76ab.
( http://commondatastorage.googleapis.com/cpp-netlib-downloads/0.11.0/cpp-netlib-0.11.0.tar.gz )

```
70c70
<     set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -ftemplate-dempth=256")

---
>     set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -ftemplate-depth=256")
```
