Minor improvements to 6.0 upgrade doc [ci skip] (#446)

* Fix typo
* Improve header description about default configuration
* Titlecase "Ruby"

Author: carlosantoniodasilva

docs/upgrading-to-6-0.md

@@ -29,7 +29,7 @@ Prior to 6.0.0, the response would NOT include a `X-Frame-Options` header since
 
 ## `ContentSecurityPolicyConfig#merge` and `ContentSecurityPolicyReportOnlyConfig#merge` work more like `Hash#merge`
 
-These classes are typically not directly instantiated by users of SecureHeaders. But, if you access `config.csp` you end up accessing one of these objects. Prior to 6.0.0, `#merge` worked more like `#append` in that it would combine policies (i.e. if both policies contained the same key the values would be combined rather than overwritten). This was not consistent with `#merge!`, which worked more like ruby's `Hash#merge!` (overwriting duplicate keys). As of 6.0.0, `#merge` works the same as `#merge!`, but returns a new object instead of mutating `self`.
+These classes are typically not directly instantiated by users of SecureHeaders. But, if you access `config.csp` you end up accessing one of these objects. Prior to 6.0.0, `#merge` worked more like `#append` in that it would combine policies (i.e. if both policies contained the same key the values would be combined rather than overwritten). This was not consistent with `#merge!`, which worked more like Ruby's `Hash#merge!` (overwriting duplicate keys). As of 6.0.0, `#merge` works the same as `#merge!`, but returns a new object instead of mutating `self`.
 
 ## `Configuration#get` has been removed
 
@@ -39,12 +39,12 @@ This method is not typically directly called by users of SecureHeaders. Given th
 
 Prior to 6.0.0 SecureHeaders pre-built and cached the headers that corresponded to the default configuration. The same was also done for named overrides. However, now that named overrides are applied dynamically, those can no longer be cached. As a result, caching has been removed in the name of simplicity. Some micro-benchmarks indicate this shouldn't be a performance problem and will help to eliminate a class of bugs entirely.
 
-## Configuration the default configuration more than once will result in an Exception
+## Calling the default configuration more than once will result in an Exception
 
 Prior to 6.0.0 you could conceivably, though unlikely, have `Configure#default` called more than once. Because configurations are dynamic, configuring more than once could result in unexpected behavior. So, as of 6.0.0 we raise `AlreadyConfiguredError` if the default configuration is setup more than once.
 
 ## All user agent sniffing has been removed
 
 The policy configured is the policy that is delivered in terms of which directives are sent. We still dedup, strip schemes, and look for other optimizations but we will not e.g. conditionally send `frame-src` / `child-src` or apply `nonce`s / `unsafe-inline`.
 
-The primary reason for these per-browser customization was to reduce console warnings. This has lead to many bugs and results inc confusing behavior. Also, console logs are incredibly noisy today and increasingly warn you about perfectly valid things (like sending `X-Frame-Options` and `frame-ancestors` together).
+The primary reason for these per-browser customization was to reduce console warnings. This has lead to many bugs and results in confusing behavior. Also, console logs are incredibly noisy today and increasingly warn you about perfectly valid things (like sending `X-Frame-Options` and `frame-ancestors` together).