core: fix spelling in Ruby files

core/array/pack/a_spec.rb

@@ -27,7 +27,7 @@
     ["abc"].pack("A*").should == "abc"
   end
 
-  it "padds the output with spaces when the count exceeds the size of the String" do
+  it "pads the output with spaces when the count exceeds the size of the String" do
     ["abc"].pack("A6").should == "abc   "
   end
 
@@ -55,7 +55,7 @@
     ["abc"].pack("a*").should == "abc"
   end
 
-  it "padds the output with NULL bytes when the count exceeds the size of the String" do
+  it "pads the output with NULL bytes when the count exceeds the size of the String" do
     ["abc"].pack("a6").should == "abc\x00\x00\x00"
   end
 

core/array/pack/z_spec.rb

@@ -26,7 +26,7 @@
     ["abc"].pack("Z*").should == "abc\x00"
   end
 
-  it "padds the output with NULL bytes when the count exceeds the size of the String" do
+  it "pads the output with NULL bytes when the count exceeds the size of the String" do
     ["abc"].pack("Z6").should == "abc\x00\x00\x00"
   end
 

core/kernel/open_spec.rb

@@ -106,7 +106,7 @@
       ScratchPad.clear
     end
 
-    it "calls #to_path to covert the argument to a String before calling #to_str" do
+    it "calls #to_path to convert the argument to a String before calling #to_str" do
       obj = mock("open to_path")
       obj.should_receive(:to_path).at_least(1).times.and_return(@name)
       obj.should_not_receive(:to_str)

core/string/unpack_spec.rb

@@ -26,7 +26,7 @@
     "a".unpack("C", offset: 1).should == [nil]
   end
 
-  it "raises an ArgumentError when the offset is larget than the string" do
+  it "raises an ArgumentError when the offset is larger than the string" do
     -> { "a".unpack("C", offset: 2) }.should raise_error(ArgumentError, "offset outside of string")
   end
 end