Remove trailing slash in proxyUrl

[kevincheng96]

Infura has trouble handling requests with a trailing slash in API endpoint. INFURA/infura#221

Credit to 🍯 for the find

[kevincheng96]

Cleaned up the fix a bit by directly sanitizing trailing slashes from the proxyUrl instead of changing pathname.

[kevincheng96]

Cleaned up the fix a bit by directly sanitizing trailing slashes from the proxyUrl instead of changing pathname.

Nevermind, reverted back to the original change since it 👨‍🍳 pointed out that it's actually more correct. We'll leave pathname untouched if it's actually defined as something other than "/".