Use cc 1.0.43 or later (#608)

cc-1.0.42 should not be used as minimal dependency verison, because it
could hang on some environment during the build.

libgit2-sys/Cargo.toml

@@ -23,7 +23,7 @@ libz-sys = "1.0.22"
 
 [build-dependencies]
 pkg-config = "0.3.7"
-cc = { version = "1.0.42", features = ['parallel'] }
+cc = { version = "1.0.43", features = ['parallel'] }
 
 [target.'cfg(unix)'.dependencies]
 openssl-sys = { version = "0.9", optional = true }