refactor(awclient, s3client, stsclient): clarify newHttpClient params

The lack of spaces around `&` made this harder to read.

My first reading of:

    &"

is the beginning of a strformat [1] format string, but my first reading
of

    & "

is string concatenation.

[1] https://nim-lang.org/docs/strformat.html

nimutils/awsclient.nim

@@ -98,7 +98,7 @@ proc newAwsClient*(creds: AwsCredentials, region,
   let
     # TODO - use some kind of template and compile-time variable to put the correct kernel used to build the sdk in the UA?
     httpclient = createHttpClient(
-      userAgent = "nimaws-sdk/0.3.3; "&defUserAgent.replace(" ", "-").toLower&"; darwin/16.7.0",
+      userAgent = "nimaws-sdk/0.3.3; " & defUserAgent.replace(" ", "-").toLower() & "; darwin/16.7.0",
     )
     scope = AwsScope(date: getAmzDateString(), region: region, service: service)
 

nimutils/s3client.nim

@@ -29,8 +29,10 @@ proc newS3Client*(creds: AwsCredentials, region: string = defaultRegion,
     host: string = awsURI, timeoutMilliseconds = 1000): S3Client =
   let
     # TODO - use some kind of template and compile-time variable to put the correct kernel used to build the sdk in the UA?
-    httpclient = newHttpClient("nimaws-sdk/0.3.3; "&defUserAgent.replace(" ",
-        "-").toLower&"; darwin/16.7.0", timeout = timeoutMilliseconds)
+    httpclient = newHttpClient(
+      "nimaws-sdk/0.3.3; " & defUserAgent.replace(" ", "-").toLower() & "; darwin/16.7.0",
+      timeout = timeoutMilliseconds,
+    )
     scope = AwsScope(date: getAmzDateString(), region: region, service: "s3")
 
   var

nimutils/stsclient.nim

@@ -14,8 +14,10 @@ proc newStsClient*(creds: AwsCredentials,
                    timeoutMilliseconds = 1000): StsClient =
   let
     # TODO - use some kind of template and compile-time variable to put the correct kernel used to build the sdk in the UA?
-    httpclient = newHttpClient("nimaws-sdk/0.3.3; "&defUserAgent.replace(" ", "-").toLower&"; darwin/16.7.0",
-                               timeout = timeoutMilliseconds)
+    httpclient = newHttpClient(
+      "nimaws-sdk/0.3.3; " & defUserAgent.replace(" ", "-").toLower() & "; darwin/16.7.0",
+      timeout = timeoutMilliseconds,
+    )
     scope = AwsScope(date: getAmzDateString(), region: region, service: "sts")
 
   var