doc: fix typo in OverflowInt godoc

Change-Id: I426310e0c05c2b4a0123299ade0fe11721d40b10
GitHub-Last-Rev: 651c0291d6f2561e3e179a0b97e0e73ac6d21e2f
GitHub-Pull-Request: golang/go#23801
Reviewed-on: https://go-review.googlesource.com/93475Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/reflect/value.go

@@ -1228,7 +1228,7 @@ func overflowFloat32(x float64) bool {
 }
 
 // OverflowInt reports whether the int64 x cannot be represented by v's type.
-// It panics if v's Kind is not Int, Int8, int16, Int32, or Int64.
+// It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.
 func (v Value) OverflowInt(x int64) bool {
 	k := v.kind()
 	switch k {