fix make check and fix usage with node 0.10

[bahamas10]

$ make check
deps/javascriptlint/build/install/jsl --nologo --nosummary --conf=tools/jsl.node.conf lib/index.js lib/verify.js lib/utils.js lib/parser.js lib/signer.js
/home/dave/dev/node-http-signature/lib/index.js
/home/dave/dev/node-http-signature/lib/verify.js
/home/dave/dev/node-http-signature/lib/utils.js
/home/dave/dev/node-http-signature/lib/parser.js
/home/dave/dev/node-http-signature/lib/signer.js
deps/jsstyle/jsstyle -f tools/jsstyle.conf lib/index.js lib/verify.js lib/utils.js lib/parser.js lib/signer.js
check ok

[trentm]

Arguably the main thing for this fix and the commit message should be about fixing node 0.10 usage, broken by #83 and released in version 1.3.0.

[trentm]

http-signature@1.3.1 is now published with this fix.