Fix safe Style/ColonMethodCall offenses

Caxlsx is using both `.` and `::`, 220 occurrences vs 280 to invoke
methods on `Axlsx` module.

This commit standardizes the approach towards `.`, which will also allow
shorter lines.

Performance is not affected

```
Comparison:
      Axlsx.validate:  8515252.3 i/s
     Axlsx::validate:  8512863.7 i/s - same-ish: difference falls within error 
```

1 files changed, 12 insertions, 12 deletions

diff --git a/lib/axlsx/stylesheet/font.rb b/lib/axlsx/stylesheet/font.rb
index 2d9647af..bb80fbc2 100644
--- a/lib/axlsx/stylesheet/font.rb
+++ b/lib/axlsx/stylesheet/font.rb
@@ -112,38 +112,38 @@ module Axlsx
     attr_reader :sz
 
     # @see name
-    def name=(v) Axlsx::validate_string v; @name = v end
+    def name=(v) Axlsx.validate_string v; @name = v end
     # @see charset
-    def charset=(v) Axlsx::validate_unsigned_int v; @charset = v end
+    def charset=(v) Axlsx.validate_unsigned_int v; @charset = v end
     # @see family
-    def family=(v) Axlsx::validate_unsigned_int v; @family = v end
+    def family=(v) Axlsx.validate_unsigned_int v; @family = v end
     # @see b
-    def b=(v) Axlsx::validate_boolean v; @b = v end
+    def b=(v) Axlsx.validate_boolean v; @b = v end
     # @see i
-    def i=(v) Axlsx::validate_boolean v; @i = v end
+    def i=(v) Axlsx.validate_boolean v; @i = v end
 
     # @see u
     def u=(v)
       v = :single if v == true || v == 1 || v == :true || v == 'true'
       v = :none if v == false || v == 0 || v == :false || v == 'false'
-      Axlsx::validate_cell_u v
+      Axlsx.validate_cell_u v
       @u = v
     end
 
     # @see strike
-    def strike=(v) Axlsx::validate_boolean v; @strike = v end
+    def strike=(v) Axlsx.validate_boolean v; @strike = v end
     # @see outline
-    def outline=(v) Axlsx::validate_boolean v; @outline = v end
+    def outline=(v) Axlsx.validate_boolean v; @outline = v end
     # @see shadow
-    def shadow=(v) Axlsx::validate_boolean v; @shadow = v end
+    def shadow=(v) Axlsx.validate_boolean v; @shadow = v end
     # @see condense
-    def condense=(v) Axlsx::validate_boolean v; @condense = v end
+    def condense=(v) Axlsx.validate_boolean v; @condense = v end
     # @see extend
-    def extend=(v) Axlsx::validate_boolean v; @extend = v end
+    def extend=(v) Axlsx.validate_boolean v; @extend = v end
     # @see color
     def color=(v) DataTypeValidator.validate "Font.color", Color, v; @color = v end
     # @see sz
-    def sz=(v) Axlsx::validate_unsigned_int v; @sz = v end
+    def sz=(v) Axlsx.validate_unsigned_int v; @sz = v end
 
     # Serializes the object
     # @param [String] str