Jonathan Singleton is about to be one phone call away from making his major-league debut. The 21-year-old first baseman_was promoted Sunday to Class AAA Oklahoma City. Singleton’s stint with the RedHawks will mark the first time he’s played above AA in his career. He’s scheduled to bat fifth and play first against the Round Rock Express in OKC. Singleton, who’s one of the Astros’ top prospects, recently spent 11 games with the Class AA Corpus Christi Hooks, hitting .263 with two home runs, eight RBIs and a .922 OPS. He’s batting a combined .271 with five homers and 13 RBIs this season after serving a 50-game suspension for a failed [...]