Ensure all strings with spaces are quoted in logs

The current logic covers the case when the log data is already a `String` instance, but not when the data is some other object that, when interpolated into the log string, results in a string containing spaces.

The example that led me here is where an exception is logged and the exception's message contains spaces. The exception gets interpolated into the string and has `to_s` called on it. [`Exception#to_s`](https://ruby-doc.org/core-2.6.5/Exception.html#method-i-to_s) returns the message, so the message (with its spaces) go into the log line, but it's bypassed the logic that adds quotes.

I used `"#{v}"` instead of `v.to_s` because it seems there is a [subtle difference in their behaviour](https://github.com/ruby/spec/blob/master/language/string_spec.rb#L147-L158), to cover the rare case where `to_s` doesn't return a string. I think we want to keep the existing behaviour here.

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 
 ## [Unreleased]
 ### Changed
+  - Ensure all strings with spaces are quoted in logs. ([#332](https://github.com/interagent/pliny/pull/332))
   - Allow ActiveSupport 5 or 6. ([#331](https://github.com/interagent/pliny/pull/331))
 
 ### Fixed

lib/pliny/log.rb

@@ -146,12 +146,15 @@ def unparse_pair(k, v)
         k
       elsif v.is_a?(Float)
         "#{k}=#{format("%.3f", v)}"
-      elsif v.is_a?(String) && v =~ /\s/
-        quote_string(k, v)
       elsif v.is_a?(Time)
         "#{k}=#{v.iso8601}"
       else
-        "#{k}=#{v}"
+        v = "#{v}"
+        if v =~ /\s/
+          quote_string(k, v)
+        else
+          "#{k}=#{v}"
+        end
       end
     end
   end

spec/log_spec.rb

@@ -176,5 +176,19 @@ def to_s
       end
       Pliny.log(foo: klass.new)
     end
+
+    it "quotes strings that are generated from object interpolation" do
+      expect(@io).to receive(:print).with("foo=\"message with space\"\n")
+      expect(@io).to receive(:print).with("foo=\"bar with space\"\n")
+
+      Pliny.log(foo: StandardError.new("message with space"))
+
+      klass = Class.new do
+        def to_s
+          "bar with space"
+        end
+      end
+      Pliny.log(foo: klass.new)
+    end
   end
 end