fix spacing in -i pres 5

2019/2019-09-09_testCourseAdv/slides/rebase-iPresentation5.md

 ## Interactive Rebase Workshop
 
 * reword the first commit's message to:  
-`These are the two squashed commits`
+`These are the two squashed commits`  
 * combine the second and first commit into one,  
 omitting the second's commit message.