Passing key as string

In ruby 1.8 struct members are strings but in 1.9 they are symbols.
cpu in $cpu_array has keys in string so I changed that symbols are converted to strings

@ ruby 1.8 http://ruby-doc.org/core-1.8.7/Struct.html#method-i-members
````
1.8.7 :015 > struct.members
 => ["fpu", "bogomips", "model", "processor", "siblings", "cache_alignment", "initial_apicid", "cpuid_level", "wp", "flags", "apicid", "fpu_exception", "cpu_mhz", "clflush_size", "address_sizes", "microcode", "power_management", "physical_id", "core_id", "vendor_id", "cpu_family", "model_name", "stepping", "cache_size", "cpu_cores"]
```
@ ruby 1.9 and 2.0 http://ruby-doc.org/core-1.9.3/Struct.html#method-i-members
```
1.9.3p392 :011 > struct.members
 => [:processor, :vendor_id, :cpu_family, :model, :model_name, :stepping, :microcode, :cpu_mhz, :cache_size, :physical_id, :siblings, :core_id, :cpu_cores, :apicid, :initial_apicid, :fpu, :fpu_exception, :cpuid_level, :wp, :flags, :bogomips, :clflush_size, :cache_alignment, :address_sizes, :power_management] 
```