patch 9.0.0828: various typos

Problem:    Various typos.
Solution:   Correct typos. (closes #11432)
diff --git a/src/INSTALLpc.txt b/src/INSTALLpc.txt
index 104cb8e..410abb6 100644
--- a/src/INSTALLpc.txt
+++ b/src/INSTALLpc.txt
@@ -72,7 +72,7 @@
 
 Visual Studio installed a batch file called vcvarsall.bat, which you must
 run to set up paths for nmake and MSVC.  We provide a batch file
-"msvc2015.bat" for this.  You may need to edit it if you didn't instal Visual
+"msvc2015.bat" for this.  You may need to edit it if you didn't install Visual
 Studio in the standard location.
 If you use VS2017 or later, you can use "msvc-latest.bat" (or "msvc2017.bat"
 and so on for the specific version).  You must specify the architecture (e.g.