Pachyderm: Fix request bodies form parameters not being percent-escaped

Fixes #65

Pachyderm/Request/Parameter.swift

@@ -67,8 +67,11 @@ extension Parameter: CustomStringConvertible {
 extension Array where Element == Parameter {
     var urlEncoded: String {
         return compactMap {
-            guard let value = $0.value else { return nil }
+            guard let value = $0.value,
-            return "\($0.name)=\(value)"
+                let escapedValue = value.addingPercentEncoding(withAllowedCharacters: .alphanumerics) else {
+                    return nil
+            }
+            return "\($0.name)=\(escapedValue)"
         }.joined(separator: "&")
     }