Loosen assertion in getting-started.asciidoc

We were asserting that the size of an index had a decimal point but it
doesn't always:
https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+5.0+java9-periodic/240/console

docs/reference/getting-started.asciidoc

@@ -607,7 +607,7 @@ And the response:
 health status index uuid                   pri rep docs.count docs.deleted store.size pri.store.size
 yellow open   bank  l7sSYV2cQXmu6_4rJWVIww   5   1       1000            0    128.6kb        128.6kb
 --------------------------------------------------
-// TESTRESPONSE[s/128.6kb/\\d+\\.\\d+[mk]?b/]
+// TESTRESPONSE[s/128.6kb/\\d+(\\.\\d+)?[mk]?b/]
 // TESTRESPONSE[s/l7sSYV2cQXmu6_4rJWVIww/.+/ _cat]
 
 Which means that we just successfully bulk indexed 1000 documents into the bank index (under the account type).