fix the cmake cmd with wrong path

[NeoZhangJianyu]

Description

The examples of CMake is with wrong path

Before change, you will meet following error print:

CMake Error: The source directory "/path/to/incubator-mxnet/build" does not appear to contain CMakeLists.txt.
Specify --help for usage, or press the help button on the CMake GUI.

After change:

-- The C compiler identification is GNU 7.4.0
-- The CXX compiler identification is GNU 7.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features

Checklist

Essentials

Changes

Document is updated

Comments

Fix the wrong path in cmake cmd.

[abhinavs95]

Thanks for the fix @NeoZhangJianyu

[abhinavs95]

@mxnet-label-bot add [Doc, pr-awaiting-review]

[pengzhao-intel]

Thanks for the fix.
Could you paste the log before and after the fix?

[NeoZhangJianyu]

Thanks for the fix.
Could you paste the log before and after the fix?

Yes, I update the log in issue description.

[TaoLv]

LGTM. Thank you for the contribution.

[pengzhao-intel]

Thanks for your contribution. Merging now.

[pengzhao-intel]

LGTM