Added NULL safety checks

These were reported as potential flaws by VeraCode scan.
Fixed potential memory leak
```clean_paths``` is deprecated in CocoaPods. Use preserve_paths instead.
update podspec to version 1.6.2
Merge pull request #103 from nickcheng/patch-1

clean_paths is deprecated in CocoaPods. Use preserve_paths instead...
Merge pull request #100 from lixar/veracode-fixes

Added NULL safety checks
Guard around dispatch_resume() being called with null pointer, as warned by the static analyzer.
Add .DS_Store to .gitignore
Merge pull request #110 from rivera-ernesto/master

Add .DS_Store to .gitignore
Fixing issue #101 : Colors in greyscale color-space do not work
Updating sample code to test grayscale color customization
Merge pull request #107 from realestate-com-au/master

Guard around dispatch_resume() being called with null pointer, as warned by the static analyzer.
Fixed a Thread issue that is already opened in the upstream.

https://github.com/denivip/CocoaLumberjack/commit/92842ea688e56ba99ab003aa4046a614219208e7